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This is a primer for producing documents in HTML, the
hypertext markup language used on the World Wide
Web. This guide is intended to be an introduction to
using HTML and creating files for the Web. You should
also check your local bookstore; there are many volumes
about the Web and HTML that could be useful.
Getting Started
Terms to Know
What Isn't Covered
HTML Version
HTML Documents
What an HTML Document Is
HTML Editors
Getting Your Files on a Server
Tags Explained
The Minimal HTML Document
A Teaching Tool
Markup Tags
HTML
HEAD
TITLE
BODY
Headings
Paragraphs
Lists
Preformatted Text
Extended Quotations
Addresses
Forced Line Breaks/Postal Addresses
Horizontal Rules
Character Formatting
Logical Versus Physical Styles
Escape Sequences
Linking
Relative Pathnames Versus Absolute Pathnames
URLs
Links to Specific Sections
Mailto
Inline Images
Aligning Images
Alternate Text for Images
Background Graphics
Background Color
External Images, Sounds, and Animations
Tables
Table Tags
General Table Format
Tables for Nontabular Information
Fill-out Forms
Troubleshooting
Avoid Overlapping Tags
Embed Only Anchors and Character Tags
Do the Final Steps
Commenting Your Files
For More Information
Style Guides
Other Introductory Documents
Additional Online References
Getting Started
Terms to Know
WWW World Wide Web
SGML Standard Generalized Markup Language--a standard
for describing markup languages
DTD Document Type Definition--this is the formal specification
of a markup language, written using SGML
HTML HyperText Markup Language--HTML is an SGML DTD
In practical terms, HTML is a collection of platform-independent
styles (indicated by markup tags) that
define the various components of a World Wide Web document.
HTML was invented by Tim
Berners-Lee while at CERN, the European Laboratory
for Particle Physics in Geneva.
What Isn't Covered
This primer assumes that you:
know how to use NCSA Mosaic or some other Web browser
have a general understanding of how Web servers and
client browsers work
have access to a Web server (or that you want to produce
HTML documents for personal use in
local-viewing mode)
HTML Version
This guide reflects the most current specification--HTML
Version 2.0-- plus some additional features that have
been widely and consistently implemented in browsers.
Future versions and new features for HTML are under
development.
HTML Documents
What an HTML Document Is
HTML documents are plain-text (also known as ASCII)
files that can be created using any text editor (e.g.,
Emacs or vi on UNIX machines; BBEdit on a Macintosh;
Notepad on a Windows machine). You can also use.
word-processing software if you remember to save your
document as "text only with line breaks."
HTML Editors
Some WYSIWYG editors are available (e.g., HotMetal,
which is available for several platforms or Adobe
PageMill for Macintoshes). You may wish to try one
of them after you learn some of the basics of HTML
tagging. It is useful to know enough HTML to code a
document before you determine the usefulness of a
WYSIWYG editor.
If you haven't already selected your software, refer
to an online listing of HTML editors (organized by
platform) to help you in your search for appropriate
software.
Getting Your Files on a Server
If you have access to a Web server at school or work,
contact your webmaster (the individual who maintains
the server) to see how you can get your files on the
Web. If you do not have access to a server at work
or
school, check to see if your community operates a FreeNet,
a community-based network that provides free
access to the Internet. Lacking a FreeNet, you may
need to contact a local Internet provider that will
post your
files on a server for a fee. (Check your local newspaper
for advertisements or with your Chamber of
Commerce for the names of companies.)
Tags Explained
An element is a fundamental component of the structure
of a text document. Some examples of elements are
heads, tables, paragraphs, and lists. Think of it this
way: you use HTML tags to mark the elements of a file
for
your browser. Elements can contain plain text, other
elements, or both.
To denote the various elements in an HTML document,
you use tags. HTML tags consist of a left angle
bracket (<), a tag name, and a right angle bracket
(>). Tags are usually paired (e.g., <H1> and
</H1>) to start
and end the tag instruction. The end tag looks just
like the start tag except a slash (/) precedes the
text within
the brackets. HTML tags are listed below.
Some elements may include an attribute, which is additional
information that is included inside the start tag.
For example, you can specify the alignment of images
(top, middle, or bottom) by including the appropriate
attribute with the image source HTML code. Tags that
have optional attributes are noted below.
NOTE: HTML
is not case sensitive. <title> is equivalent
to <TITLE> or <TiTlE>. There are a few
exceptions noted in Escape Sequences below.
Not all tags are supported by all World Wide Web browsers.
If a browser does not support a tag, it (usually)
just ignores it.
The Minimal HTML Document
Every HTML document should contain certain standard
HTML tags. Each document consists of head and
body text. The head contains the title, and the body
contains the actual text that is made up of paragraphs,
lists,
and other elements. Browsers expect specific information
because they are programmed according to HTML
and SGML specifications.
Required elements are shown in this sample bare-bones
document:
<html>
<head>
<TITLE>A Simple HTML Example</TITLE>
</head>
<body>.<H1>HTML is Easy To Learn</H1>
<P>Welcome to the world of HTML.
This is the first paragraph. While short it is
still a paragraph!</P>
<P>And this is the second paragraph.</P>
</body>
</html>
The required elements are the <html>, <head>,
<title>, and <body> tags (and their corresponding
end tags).
Because you should include these tags in each file,
you might want to create a template file with them.
(Some
browsers will format your HTML file correctly even
if these tags are not included. But some browsers won't!
So make sure to include them.)
Click to see the formatted version of the example.
A longer example is also available but you should read
through the rest of the guide before you take a look.
This longer-example file contains tags explained in
the
next section.
A Teaching Tool
To see a copy of the file that your browser reads to
generate the information in your current window, select
View Source (or the equivalent) from the browser menu.
The file contents, with all the HTML tags, are
displayed in a new window.
This is an excellent way to see how HTML is used and
to learn tips and constructs. Of course, the HTML
might not be technically correct. Once you become familiar
with HTML and check the many online and
hard-copy references on the subject, you will learn
to distinguish between "good" and "bad"
HTML.
Remember that you can save a source file with the HTML
codes and use it as a template for one of your Web
pages or modify the format to suit your purposes.
Markup Tags
HTML
This element tells your browser that the file contains
HTML-coded information. The file extension .html also
indicates this an HTML document and must be used. (If
you are restricted to 8.3 filenames (e.g.,
LeeHome.htm, use only .htm for your extension.)
HEAD
The head element identifies the first part of your
HTML-coded document that contains the title. The title
is
shown as part of your browser's window (see below).
TITLE
The title element contains your document title and
identifies its content in a global context. The title
is displayed
somewhere on the browser window (usually at the top),
but not within the text area. The title is also what
is
displayed on someone's hotlist or bookmark list, so
choose something descriptive, unique, and relatively
short. A title is also used during a WAIS search of
a server.
For example, you might include a shortened title of
a book along with the chapter contents: NCSA Mosaic
Guide (Windows): Installation. This tells the software
name, the platform, and the chapter contents, which
is
more useful than simply calling the document Installation.
Generally you should keep your titles to 64
characters or fewer.
BODY.
The second--and largest--part of your HTML document
is the body, which contains the content of your
document (displayed within the text area of your browser
window). The tags explained below are used within
the body of your HTML document.
Headings
HTML has six levels of headings, numbered 1 through
6, with 1 being the most prominent. Headings are
displayed in larger and/or bolder fonts than normal
body text. The first heading in each document should
be
tagged <H1>.
The syntax of the heading element is:
<Hy>Text of heading </Hy>
where y is a number between 1 and 6 specifying the
level of the heading.
Do not skip levels of headings in your document. For
example, don't start with a level-one heading (<H1>)
and then next use a level-three (<H3>) heading.
Paragraphs
Unlike documents in most word processors, carriage
returns in HTML files aren't significant. So you don't
have to worry about how long your lines of text are
(better to have them fewer than 72 characters long
though). Word wrapping can occur at any point in your
source file, and multiple spaces are collapsed into
a
single space by your browser.
In the bare-bones example shown in the Minimal HTML
Document section, the first paragraph is coded as
<P>Welcome to the world of HTML.
This is the first paragraph.
While short it is
still a paragraph!</P>
In the source file there is a line break between the
sentences. A Web browser ignores this line break and
starts
a new paragraph only when it encounters another <P>
tag.
Important:
You must indicate paragraphs with <P> elements.
A browser ignores any indentations or blank
lines in the source text. Without <P> elements,
the document becomes one large paragraph. (One exception
is
text tagged as "preformatted," which is explained
below.) For example, the following would produce identical
output as the first bare-bones HTML example:
<H1>Level-one heading</H1>
<P>Welcome to the world of HTML.</P>
This is the
first paragraph. While short it is still a
paragraph! </P> <P>And this is the second
paragraph.</P>
To preserve readability in HTML files, put headings
on separate lines, use a blank line or two where it
helps
identify the start of a new section, and separate paragraphs
with blank lines (in addition to the <P> tags).
These
extra spaces will help you when you edit your files
(but your browser will ignore the extra spaces because
it
has its own set of rules on spacing that do not depend
on the spaces you put in your source file).
NOTE:
The </P> closing tag can be omitted. This is
because browsers understand that when they encounter
a
<P> tag, it implies that there is an end to the
previous paragraph.
Using the <P> and </P> as a paragraph container
means that you can center a paragraph by including
the
ALIGN=alignment attribute in your source file..<P
ALIGN=CENTER>
This is a centered paragraph.
[See the formatted version below.]
</P>
This is a centered paragraph.
Lists
HTML supports unnumbered, numbered, and definition
lists. You can nest lists too, but use this feature
sparingly because too many nested items can get difficult
to follow.
Unnumbered Lists
To make an unnumbered, bulleted list,
1. start with an opening list <UL> (for unnumbered
list) tag
2. enter the <LI> (list item) tag followed by
the individual item; no closing </LI> tag is
needed
3. end the entire list with a closing list </UL>
tag
Below is a sample three-item list:
<UL>
<LI> apples
<LI> bananas
<LI> grapefruit
</UL>
The output is:
apples
bananas
grapefruit
The <LI> items can contain multiple paragraphs.
Indicate the paragraphs with the <P> paragraph
tags.
Numbered Lists
A numbered list (also called an ordered list, from
which the tag name derives) is identical to an unnumbered
list, except it uses <OL> instead of <UL>.
The items are tagged using the same <LI> tag.
The following HTML
code:
<OL>
<LI> oranges
<LI> peaches
<LI> grapes
</OL>
produces this formatted output:
1. oranges
2. peaches
3. grapes
Definition Lists
A definition list (coded as <DL>) usually consists
of alternating a definition term (coded as <DT>)
and a.definition
definition (coded as <DD>). Web browsers generally
format the definition on a new line.
The following is an example of a definition list:
<DL>
<DT> UIUC
<DD> University of Manchester at Urbana-Champaign
is one of three campuses of the University of Manchester
system
<DT> UIC
<DD> University of Manchester at Chicago is another
campus
<DT> UIS
<DD> University of Manchester at springfield
is the newest
campus in the system
</DL>
The output looks like:
UIUC
University of Manchester at Urbana-Champaign is one
of three campuses of the University of Manchester system
UIC
University of Manchester at Chicago is another campus
UIS
University of Manchester at Springfield is the newest
campus in the system
The <DT> and <DD> entries can contain multiple
paragraphs (indicated by <P> paragraph tags),
lists, or other
definition information.
The COMPACT attribute can be used routinely in case
your definition terms are very short. If, for example,
you
are showing some computer options, the options may
fit on the same line as the start of the definition.
<DL COMPACT>
<DT> -i
<DD>invokes NCSA Mosaic for Microsoft Windows
using the initialization file defined in the path
<DT> -k
<DD>invokes NCSA Mosaic for Microsoft Windows
in
kiosk mode
</DL>
The output looks like:
-i invokes NCSA Mosaic for Microsoft Windows using
the initialization file defined in the path.
-k invokes NCSA Mosaic for Microsoft Windows in kiosk
mode.
Nested Lists
Lists can be nested. You can also have a number of
paragraphs, each containing a nested list, in a single
list
item.
Here is a sample nested list:
<UL>
<LI> A few New England states:
<UL>
<LI> Vermont
<LI> New Hampshire.<LI> Maine
</UL>
<LI> Two Midwestern states:
<UL>
<LI> Michigan
<LI> Indiana
</UL>
</UL>
The nested list is displayed as
A few New England states:
Vermont
New Hampshire
Maine
Two Midwestern states:
Michigan
Indiana
Preformatted Text
Use the <PRE> tag (which stands for "preformatted")
to generate text in a fixed-width font. This tag also
makes spaces, new lines, and tabs significant (multiple
spaces are displayed as multiple spaces, and lines
break
in the same locations as in the source HTML file).
This is useful for program listings, among other things.
For
example, the following lines:
<PRE>
#!/bin/csh
cd $SCR
cfs get mysrc.f:mycfsdir/mysrc.f
cfs get myinfile:mycfsdir/myinfile
fc -02 -o mya.out mysrc.f
mya.out
cfs save myoutfile:mycfsdir/myoutfile
rm *
</PRE>
display as:
#!/bin/csh
cd $SCR
cfs get mysrc.f:mycfsdir/mysrc.f
cfs get myinfile:mycfsdir/myinfile
fc -02 -o mya.out mysrc.f
mya.out
cfs save myoutfile:mycfsdir/myoutfile
rm *
The <PRE> tag can be used with an optional WIDTH
attribute that specifies the maximum number of characters
for a line. WIDTH also signals your browser to choose
an appropriate font and indentation for the text.
Hyperlinks can be used within <PRE> sections.
You should avoid using other HTML tags within <PRE>
sections, however.
Note that because <, >, and & have special
meanings in HTML, you must use their escape sequences
(<,
>, and &, respectively) to enter these
characters. See the section Escape Sequences for more
information.
Extended Quotations.
Use the <BLOCKQUOTE> tag to include lengthy quotations
in a separate block on the screen.
Most browsers
generally change the margins for the quotation to separate
it from surrounding text.
In the example:
<BLOCKQUOTE>
<P>Omit needless words.</P>
<P>Vigorous writing is concise. A sentence should
contain no unnecessary words, a paragraph no unnecessary
sentences, for the same reason that a drawing should
have
no unnecessary lines and a machine no unnecessary parts.
</BLOCKQUOTE>
the result is:
Omit needless words.
Vigorous writing is concise. A sentence should contain
no unnecessary words, a paragraph
no unnecessary sentences, for the same reason that
a drawing should have no unnecessary
lines and a machine no unnecessary parts.
Addresses
The <ADDRESS> tag is generally used to specify
the author of a document, a way to contact the author
(e.g., an
email address), and a revision date. It is usually
the last item in a file.
For example, the last line of the online version of
this guide is:
<ADDRESS>
A Beginner's Guide to HTML / NCSA /
pubs@ncsa.uiuc.edu / revised April 96
</ADDRESS>
The result is:
A Beginner's Guide to HTML / NCSA / pubs@ncsa.uiuc.edu
/ revised April 96
NOTE: <ADDRESS> is not used for postal addresses.
See "Forced Line Breaks" below to see how
to format
postal addresses.
Forced Line Breaks/Postal Addresses
The <BR> tag forces a line break with no extra
(white) space between lines. Using <P> elements
for short lines
of text such as postal addresses results in unwanted
additional white space. For example, with <BR>:
National Center for Supercomputing Applications<BR>
605 East Springfield Avenue<BR>
Champaign, Illinois 61820-5518<BR>
The output is:
National Center for Supercomputing Applications.605
East Springfield Avenue
Champaign, Illinois 61820-5518
Horizontal Rules
The <HR> tag produces a horizontal line the width
of the browser window. A horizontal rule is useful
to
separate sections of your document. For example, many
people add a rule at the end of their text and before
the
<address> information.
You can vary a rule's size (thickness) and width (the
percentage of the window covered by the rule).
Experiment with the settings until you are satisfied
with the presentation. For example:
<HR SIZE=4 WIDTH="50%">
displays as:
Character Formatting
HTML has two types of styles for individual words or
sentences: logical and physical. Logical styles tag
text
according to its meaning, while physical styles indicate
the specific appearance of a section. For example,
in
the preceding sentence, the words "logical styles"
was tagged as a "definition." The same effect
(formatting
those words in italics) could have been achieved via
a different tag that tells your browser to "put
these words
in italics."
NOTE:
Some browsers don't attach any style to the <DFN>
tag, so you might not see the indicated phrases in
the previous paragraph in italics.
Logical Versus Physical Styles
If physical and logical styles produce the same result
on the screen, why are there both?
In the ideal SGML universe, content is divorced from
presentation. Thus SGML tags a level-one heading as
a
level-one heading, but does not specify that the level-one
heading should be, for instance, 24-point bold Times
centered. The advantage of this approach (it's similar
in concept to style sheets in many word processors)
is
that if you decide to change level-one headings to
be 20-point left-justified Helvetica, all you have
to do is
change the definition of the level-one heading in your
Web browser. Indeed many browsers today let you
define how you want the various HTML tags rendered
on-screen.
Another advantage of logical tags is that they help
enforce consistency in your documents. It's easier
to tag
something as <H1> than to remember that level-one
headings are 24-point bold Times centered or whatever.
For example, consider the <STRONG> tag. Most
browsers render it in bold text. However, it is possible
that a
reader would prefer that these sections be displayed
in red instead. Logical styles offer this flexibility.
Of course, if you want something to be displayed in
italics (for example) and do not want a browser's setting
to display it differently, use physical styles. Physical
styles, therefore, offer consistency in that something
you
tag a certain way will always be displayed that way
for readers of your document.
Try to be consistent about which type of style you
use. If you tag with physical styles, do so throughout
a
document. If you use logical styles, stick with them
within a document. Keep in mind that future releases
of
HTML might not support physical styles, which could
mean that browsers will not display physical style
coding.
Logical Styles.
<DFN> for a word being defined. Typically displayed
in italics. (NCSA Mosaic is a World Wide
Web browser.)
<EM> for emphasis. Typically displayed in italics.
(Consultants cannot reset your password unless you
call
the help line.)
<CITE> for titles of books, films, etc. Typically
displayed in italics. (A Beginner's Guide to HTML)
<CODE> for computer code. Displayed in a fixed-width
font. (The <stdio.h> header file)
<KBD> for user keyboard entry. Typically displayed
in plain fixed-width font. (Enter passwd to change
your
password.)
<SAMP> for a sequence of literal characters.
Displayed in a fixed-width font. (Segmentation fault:
Core
dumped.)
<STRONG>
for strong emphasis. Typically displayed in bold. (NOTE:
Always check your links.)
<VAR> for a variable, where you will replace
the variable with specific information. Typically displayed
in
italics. (rm filename deletes the file.)
Physical Styles
<B> bold text
<I> italic text
<TT> typewriter text, e.g. fixed-width font.Escape
Sequences (a.k.a. Character Entities)
Character entities have two functions:
escaping special characters
displaying other characters not available in the plain
ASCII character set (primarily characters with
diacritical marks)
Three ASCII characters--the left angle bracket (<),
the right angle bracket (>), and the ampersand (&)--have
special meanings in HTML and therefore cannot be used
"as is" in text. (The angle brackets are
used to indicate
the beginning and end of HTML tags, and the ampersand
is used to indicate the beginning of an escape
sequence.) Double quote marks may be used as-is but
a character entity may also be used (").
To use one of the three characters in an HTML document,
you must enter its escape sequence instead:
< the escape sequence for <
> the escape sequence for >
& the escape sequence for &
Additional escape sequences support accented characters,
such as:
ö the escape sequence for a lowercase o with
an umlaut: ö
ñ
the escape sequence for a lowercase n with an tilde:
n
È
the escape sequence for an uppercase E with a grave
accent: E
You can substitute other letters for the o, n, and
E shown above. Check this online reference for a longer
list of
special characters.
NOTE: Unlike the rest of HTML, the escape sequences
are case sensitive. You cannot, for instance, use <
instead of <.
Linking.
The chief power of HTML comes from its ability to link
text and/or an image to another document or section
of
a document. A browser highlights the identified text
or image with color and/or underlines to indicate that
it is a
hypertext link (often shortened to hyperlink or link).
HTML's single hypertext-related tag is <A>, which
stands for anchor. To include an anchor in your document:
1. start the anchor with <A (include a space after
the A)
2. specify the document you're linking to by entering
the parameter HREF="filename" followed by
a
closing right angle bracket (>)
3. enter the text that will serve as the hypertext
link in the current document
4. enter the ending anchor tag: </A> (no space
is needed before the end anchor tag)
Here is a sample hypertext reference in a file called
US.html:
<A HREF="MaineStats.html">Maine</A>
This entry makes the word Maine the hyperlink to the
document MaineStats.html, which is in the same
directory as the first document.
Relative Pathnames Versus Absolute Pathnames
You can link to documents in other directories by specifying
the relative path from the current document to the
linked document. For example, a link to a file NYStats.html
located in the subdirectory AtlanticStates
would be:
<A HREF="AtlanticStates/NYStats.html">New
York</A>
These are called relative links because you are specifying
the path to the linked file relative to the location
of the
current file. You can also use the absolute pathname
(the complete URL) of the file, but relative links
are more
efficient in accessing a server.
Pathnames use the standard UNIX syntax. The UNIX syntax
for the parent directory (the directory that
contains the current directory) is "..".
(For more information consult a beginning UNIX reference
text such as
Learning the UNIX Operating System from O'Reilly and
Associates, Inc.)
If you were in the NYStats.html file and were referring
to the original document US.html, your link would
look like this:
<A HREF="../US.html">United States</A>
In general, you should use relative links because:
1. it's easier to move a group of documents to another
location (because the relative path names will still
be valid)
2. it's more efficient connecting to the server
3. there is less to type
However use absolute pathnames when linking to documents
that are not directly related. For example,
consider a group of documents that comprise a user
manual. Links within this group should be relative
links.
Links to other documents (perhaps a reference to related
software) should use full path names. This way if you
move the user manual to a different directory, none
of the links would have to be updated.
URLs.
The World Wide Web uses Uniform Resource Locators (URLs)
to specify the location of files on other
servers. A URL includes the type of resource being
accessed (e.g., Web, gopher, WAIS), the address of
the
server, and the location of the file. The syntax is:
scheme://host.domain [:port]/path/ filename
where scheme is one of file a file on your local system
ftp a file on an anonymous FTP server
http a file on a World Wide Web server
gopher a file on a Gopher server
WAIS a file on a WAIS server
news a Usenet newsgroup
telnet a connection to a Telnet-based service
The port number can generally be omitted. (That means
unless someone tells you otherwise, leave it out.)
For example, to include a link to this primer in your
document, enter:
<A HREF="http://www.ncsa.uiuc.edu/General/Internet/WWW/HTMLPrimer.html">
NCSA's Beginner's Guide to HTML</A>
This entry makes the text NCSA's Beginner's Guide to
HTML a hyperlink to this document.
For more information on URLs, refer to:
WWW Names and Addresses, URIs, URLs, URNs
A Beginner's Guide to URLs
Links to Specific Sections
Anchors can also be used to move a reader to a particular
section in a document (either the same or a different
document) rather than to the top, which is the default.
This type of an anchor is commonly called a named
anchor because to create the links, you insert HTML
names within the document.
This guide is a good example of using named anchors
in one document. The guide is constructed as one
document to make printing easier. But as one (long)
document, it can be time-consuming to move through
when all you really want to know about is one bit of
information about HTML. Internal hyperlinks are used
to
create a "table of contents" at the top of
this document. These hyperlinks move you from one location
in the
document to another location in the same document.
(Go to the top of this document and then click on the
Links to Specific Sections hyperlink in the table of
contents. You will wind up back here.)
You can also link to a specific section in another
document. That information is presented first because
understanding that helps you understand linking within
one document.
Links Between Sections of Different Documents
Suppose you want to set a link from document A (documentA.html)
to a specific section in another document
(MaineStats.html).
Enter the HTML coding for a link to a named anchor:
documentA.html:.In addition to the many state parks,
Maine is also home to
<a href="MaineStats.html#ANP">Acadia
National Park</a>.
Think of the characters after the hash (#) mark as
a tab within the MaineStats.html file. This tab tells
your
browser what should be displayed at the top of the
window when the link is activated. In other words,
the first
line in your browser window should be the Acadia National
Park heading.
Next, create the named anchor (in this example "ANP")
in MaineStats.html:
<H2><A NAME="ANP">Acadia National
Park</a></H2>
With both of these elements in place, you can bring
a reader directly to the Acadia reference in
MaineStats.html.
NOTE:
You cannot make links to specific sections within a
different document unless either you have write
permission to the coded source of that document or
that document already contains in-document named
anchors. For example, you could include named anchors
to this primer in a document you are writing because
there are named anchors in this guide (use View Source
in your browser to see the coding). But if this
document did not have named anchors, you could not
make a link to a specific section because you cannot
edit
the original file on NCSA's server.
Links to Specific Sections within the Current Document
The technique is the same except the filename is omitted.
For example, to link to the ANP anchor from within
MaineStats, enter:
...More information about
<A HREF="#ANP">Acadia National Park</a>
is available elsewhere in this document.
Be sure to include the <A NAME=> tag at the place
in your document where you want the link to jump to
(<H2><A NAME="ANP">Acadia National
Park</a></H2>).
Named anchors are particularly useful when you think
readers will print a document in its entirety or when
you
have a lot of short information you want to place online
in one file.
Mailto
You can make it easy for a reader to send electronic
mail to a specific person or mail alias by including
the
mailto attribute in a hyperlink. The format is:
<A HREF="mailto:emailinfo@host">Name</a>
For example, enter:
<A HREF="mailto:pubs@ncsa.uiuc.edu">
NCSA Publications Group</a>
to create a mail window that is already configured
to open a mail window for the NCSA Publications Group
alias. (You, of course, will enter another mail address!).Inline
Images
Most Web browsers can display inline images (that is,
images next to text) that are in X Bitmap (XBM), GIF,
or JPEG format. Other image formats are being incorporated
into Web browsers [e.g., the Portable Network
Graphic (PNG) format]. Each image takes time to process
and slows down the initial display of a document.
Carefully select your images and the number of images
in a document.
To include an inline image, enter:
<IMG SRC=ImageName>
where ImageName is the URL of the image file.
The syntax for <IMG SRC> URLs is identical to
that used in an anchor HREF. If the image file is a
GIF file, then
the filename part of ImageName must end with .gif.
Filenames of X Bitmap images must end with .xbm;
JPEG image files must end with .jpg or .jpeg; and Portable
Network Graphic files must end with .png.
Image Size Attributes
You should include two other attributes on <IMG>
tags to tell your browser the size of the images it
is
downloading with the text. The HEIGHT and WIDTH attributes
let your browser set aside the appropriate space
(in pixels) for the images as it downloads the rest
of the file. (Get the pixel size from your image-processing
software, such as Adobe Photoshop.)
For example, to include a self portrait image in a
file along with the portrait's dimensions, enter:
<IMG SRC=SelfPortrait.gif HEIGHT=100 WIDTH=65>
NOTE:
Some browsers use the HEIGHT and WIDTH attributes to
stretch or shrink an image to fit into the
allotted space when the image does not exactly match
the attribute numbers. Not all browser developers think
stretching/shrinking is a good idea. So don't plan
on your readers having access to this feature. Check
your
dimensions and use the correct ones.
Aligning Images
You have some flexibility when displaying images. You
can have images separated from text and aligned to
the
left or right or centered. Or you can have an image
aligned with text. Try several possibilities to see
how your
information looks best.
Aligning Text with an Image
By default the bottom of an image is aligned with the
following text, as shown in this paragraph.
You can align images to the top or center of a paragraph
using the ALIGN= attributes TOP and CENTER.
This text is aligned with the top of the image (<IMG
SRC = "BarHotlist.gif" ALIGN=TOP>).
Notice how the browser aligns only one line and then
jumps to the bottom of the image for the rest of the
text..And
this text is centered on the image (<IMG SRC = "BarHotlist.gif"
ALIGN=CENTER>).
Again, only one line of text is centered; the rest
is below the image.
Images without Text
To display an image without any associated text (e.g.,
your organization's logo), make it a separate paragraph.
Use the paragraph ALIGN= attribute to center the image
or adjust it to the right side of the window as shown
below:
<p ALIGN=CENTER>
<IMG SRC = "BarHotlist.gif">
</p>
which results in:
The image is centered; this paragraph starts below
it and left justified.
Alternate Text for Images
Some World Wide Web browsers -- primarily those that
run on VT100 terminals -- cannot display images.
Some users turn off image loading even if their software
can display images (especially if they are using a
modem or have a slow connection). HTML provides a mechanism
to tell readers what they are missing on
your pages.
The ALT attribute lets you specify text to be displayed
instead of an image. For example:
<IMG SRC="UpArrow.gif" ALT="Up">
where UpArrow.gif is the picture of an upward pointing
arrow. With graphics-capable viewers that have
image-loading turned on, you see the up arrow graphic.
With a VT100 browser or if image-loading is turned
off, the word Up is shown in your window.
You should try to include alternate text for each image
you use in your document, which is a courtesy for your
readers.
Background Graphics
Newer versions of Web browsers can load an image and
use it as a background when displaying a page. Some
people like background images and some don't. In general,
if you want to include a background, make sure
your text can be read easily when displayed on top
of the image.
Background images can be a texture (linen finished
paper, for example) or an image of an object (a logo
possibly). You create the background image as you do
any image.
However you only have to create a small piece of the
image. Using a feature called tiling, a browser takes
the
image and repeats it across and down to fill your browser
window. In sum you generate one image, and the.
The tag to include a background image is included in
the <BODY> statement as an attribute:
<BODY BACKGROUND="filename.gif">
Background Color
By default browsers display text in black on a gray
background. However, you can change both elements if
you want. Some HTML authors select a background color
and coordinate it with a change in the color of the
text.
Always preview changes like this to make sure your
pages are readable. (For example, many people find
red
text on a black background difficult to read!)
You change the color of text, links, visited links,
and active links using attributes of the <BODY>
tag. For
example, enter:
<BODY BGCOLOR="#000000" TEXT="#FFFFFF"
LINK="#9690CC">
This creates a window with a black background (BGCOLOR),
white text (TEXT), and silvery hyperlinks (LINK).
The six-digit number and letter combinations represent
colors by giving their RGB (red, green, blue) value.
The six digits are actually three two-digit numbers
in sequence, representing the amount of red, green,
or blue
as a hexadecimal value in the range 00-FF. For example,
000000 is black (no color at all), FF0000 is bright
red, and FFFFFF is white (fully saturated with all
three colors). These number and letter combinations
are
cryptic. Fortunately an online resource is available
to help you track down the combinations that map to
specific colors and there is software available for
you to do this on your workstation:
ColorPro Web server
(http://www.biola.edu/cgi-bin/colorpro/)
WebColor - downloadable software site
(http://www.macworld.com/cgi-bin/software.pl/TelecomInternet/Software.767.html)
External Images, Sounds, and Animations
You may want to have an image open as a separate document
when a user activates a link on either a word or a
smaller, inline version of the image included in your
document. This is called an external image, and it
is
useful if you do not wish to slow down the loading
of the main document with large inline images.
To include a reference to an external image, enter:
<A HREF="MyImage.gif">link anchor</A>
You can also use a smaller image as a link to a larger
image. Enter:
<A HREF="LargerImage.gif"><IMG SRC="SmallImage.gif"></A>
The reader sees the SmallImage.gif image and clicks
on it to open the LargerImage.gif file.
Use the same syntax for links to external animations
and sounds. The only difference is the file extension
of
the linked file. For example,
<A HREF="AdamsRib.mov">a wonderful
Hepburn/Tracy movie</A>.specifies a link to a
QuickTime movie.
Some common file types and their extensions are:
File Type Extension
plain text .txt
HTML document .html
GIF image .gif
TIFF image .tiff
X Bitmap image .xbm
JPEG image .jpg or .jpeg
PostScript file .ps
AIFF sound file .aiff
AU sound file .au
WAV sound file .wav
QuickTime movie .mov
MPEG movie .mpeg or .mpg
Keep in mind your intended audience and their access
to software. Most UNIX workstations, for instance,
cannot view QuickTime movies.
Tables
Before HTML tags for tables were finalized, authors
had to carefully format their tabular information within
<PRE> tags, counting spaces and previewing their
output. Tables are very useful for presentation of
tabular
information as well as a boon to creative HTML authors
who use the table tags to present their regular Web
pages. (Check out the NCSA Relativity Group's pages
for an excellent, award-winning example.)
Think of your tabular information in light of the coding
explained below. A table has heads where you explain
what the columns/rows include, rows for information,
cells for each item. In the following table, the first
column contains the header information, each row explains
an HTML table tag, and each cell contains a paired
tag or an explanation of the tag's function..Table
Elements
Element Description
<TABLE> ...
</TABLE>
defines a table in HTML. If the BORDER attribute is
present, your browser displays the table with a border.
<CAPTION> ...
</CAPTION>
defines the caption for the title of the table. The
default position of the title is centered at the top
of the table.
The attribute ALIGN=BOTTOM can be used to position
the caption below the table.
NOTE:
Any kind of markup tag can be used in the caption.
<TR> ... </TR> specifies a table row within
a table. You may define default attributes for
the entire row: ALIGN (LEFT, CENTER, RIGHT) and/or
VALIGN (TOP,
MIDDLE, BOTTOM). See Table Attributes at the end of
this table for more
information.
<TH> ... </TH> defines a table header cell.
By default the text in this cell is bold and
centered. Table header cells may contain other attributes
to determine the
characteristics of the cell and/or its contents. See
Table Attributes at the
end of this table for more information.
<TD> ... </TD> defines a table data cell.
By default the text in this cell is aligned left and
centered vertically. Table data cells may contain other
attributes to
determine the characteristics of the cell and/or its
contents. See Table
Attributes at the end of this table for more information.
Table Attributes
NOTE: Attributes defined within <TH> ...
</TH> or <TD> ... </TD> cells override
the default
alignment set in a <TR> ... </TR>.
Attribute Description
ALIGN (LEFT, CENTER,
RIGHT)
VALIGN (TOP, MIDDLE,
BOTTOM)
COLSPAN=n
ROWSPAN=n
NOWRAP
Horizontal alignment of a cell.
Vertical alignment of a cell.
The number (n) of columns a cell spans.
The number (n) of rows a cell spans.
Turn off word wrapping within a cell..<TH> cell
contents </TH> first cell in row 1 (a head)
<TH> cell contents </TH> last cell in row
1 (a head)
</TR> end of first row definition
<TR> start of second row definition
<TD> cell contents </TD> first cell in
row 2
<TD> cell contents </TD> last cell in row
2
</TR> end of second row definition
<TR> start of last row definition
<TD> cell contents </TD> first cell in
last row ...
<TD> cell contents </TD> last cell in last
row
</TR> end of last row definition
</TABLE> end of table definition
The <TABLE> and </TABLE> tags must surround
the entire table definition. The first item inside
the table is the
CAPTION, which is optional. Then you can have any number
of rows defined by the <TR> and </TR> tags.
Within a row you can have any number of cells defined
by the <TD>...</TD> or <TH>...</TH>
tags. Each row
of a table is, essentially, formatted independently
of the rows above and below it. This lets you easily
display
tables like the one above with a single cell, such
as Table Attributes, spanning columns of the table.
Tables for Nontabular Information
Some HTML authors use tables to present nontabular
information. For example, because links can be included
in table cells, some authors use a table with no borders
to create "one" image from separate images.
Browsers
that can display tables properly show the various images
seamlessly, making the created image seem like an
image map (one image with hyperlinked quadrants).
Using table borders with images can create an impressive
display as well. Experiment and see what you like.
Fill-out Forms
Web forms let a reader return information to a Web
server for some action. For example, suppose you collect
names and email addresses so you can email some information
to people who request it. For each person who
enters his or her name and address, you need some information
to be sent and the respondent's particulars
added to a data base.
This processing of incoming data is usually handled
by a script or program written in Perl or another language
that manipulates text, files, and information. If you
cannot write a program or script for your incoming
information, you need to find someone who can do this
for you.
The forms themselves are not hard to code. They follow
the same constructs as other HTML tags. What could
be difficult is the program or script that takes the
information submitted in a form and processes it. Because
of
the need for specialized scripts to handle the incoming
form information, fill-out forms are not discussed
in this
primer. Check the Additional Online Reference section
for more information.
Troubleshooting
Avoid Overlapping Tags
Consider this example of HTML:
<B>This is an example of <DFN>overlapping</B>
HTML tags.</DFN>.The word overlapping is contained
within
both the <B> and <DFN> tags. A browser
might be confused by this
coding and might not display it the way you intend.
The only way to know is to check each popular browser
(which is time-consuming and impractical).
In general, avoid overlapping tags. Look at your tags
and try pairing them up. Tags (with the obvious
exceptions of elements whose end tags may be omitted,
such as paragraphs) should be paired without an
intervening tag in between. Look again at the example
above. You cannot pair the bold tags without another
tag
in the middle (the first definition tag). Try matching
your coding up like this to see if you have any problem
areas that should be fixed before your release your
files to a server.
Embed Only Anchors and Character Tags
HTML protocol allows you to embed links within other
HTML tags:
<H1><A HREF="Destination.html">My
heading</A></H1>
Do not embed HTML tags within an anchor:
<A HREF="Destination.html">
<H1>My heading</H1>
</A>
Although most browsers currently handle this second
example, the official HTML specifications do not
support this construct and your file will probably
not work with future browsers. Remember that browsers
can
be forgiving when displaying improperly coded files.
But that forgiveness may not last to the next version
of
the software! When in doubt, code your files according
to the HTML specifications (see For More Information
below).
Character tags modify the appearance of the text within
other elements:
<UL>
<LI><B>A bold list item</B>
<LI><I>An italic list item</I>
</UL>
Avoid embedding other types of HTML element tags. For
example, you might be tempted to embed a heading
within a list in order to make the font size larger:
<UL>
<LI><H1>A large heading</H1>
<LI><H2>Something slightly smaller</H2>
</UL>
Although some browsers handle this quite nicely, formatting
of such coding is unpredictable (because it is
undefined). For compatibility with all browsers, avoid
these kinds of constructs. (The Netscape <FONT>
tag,
which lets you specify how large individual characters
will be displayed in your window, is not currently
part
of the official HTML specifications.)
What's the difference between embedding a <B>
within a <LI> tag as opposed to embedding a <H1>
within a
<LI>? Within HTML the semantic meaning of <H1>
is that it's the main heading of a document and that
it
should be followed by the content of the document.
Therefore it doesn't make sense to find a <H1>
within a
list.
Character formatting tags also are generally not additive.
For example, you might expect that:.<B><I>some
text</I></B>
would produce bold-italic text. On some browsers it
does; other browsers interpret only the innermost tag.
Do the Final Steps
Validate Your Code
When you put a document on a Web server, be sure to
check the formatting and each link (including named
anchors). Ideally you will have someone else read through
and comment on your file(s) before you consider a
document finished.
You can run your coded files through an HTML validation
service that will tell you if your code conforms to
accepted HTML. If you are not sure your coding conforms
to HTML specifications, this can be a useful
teaching tool. Fortunately the service lets you select
the level of conformance you want for your files (i.e.,
strict, level 2, level 3). If you want to use some
codes that are not officially part of the HTML specifications,
this latitude is helpful.
Dummy Images
When an <IMG SRC> tag points to an image that
does not exist, a dummy image is substituted by your
browser
software. When this happens during your final review
of your files, make sure that the referenced image
does
in fact exist, that the hyperlink has the correct information
in the URL, and that the file permission is set
appropriately (world-readable). Then check online again!
Update Your Files
If the contents of a file are static (such as a biography
of George Washington), no updating is probably
needed. But for documents that are time sensitive or
covering a field that changes frequently, remember
to
update your documents!
Updating is particularly important when the file contains
information such as a weekly schedule or a deadline
for a program funding announcement. Remove out-of-date
files or note why something that appears dated is
still on a server (e.g., the program requirements will
remain the same for the next cycle so the file is still
available as an interim reference).
Browsers Differ
Web browsers display HTML elements differently. Remember
that not all codes used in HTML files are
interpreted by all browsers. Any code a browser does
not understand is usually ignored though.
You could spend a lot of time making your file "look
perfect" using your current browser. If you check
that
file using another browser, it will likely display
(a little or a lot) differently. Hence these words
of advice: code
your files using correct HTML. Leave the interpreting
to the browsers and hope for the best.
Commenting Your Files
You might want to include comments in your HTML files.
Comments in HTML are like comments in a
computer program--the text you enter is not used by
the browser in any formatting and is not directly viewable
by the reader just as computer program comments are
not used and are not viewable. The comments are
accessible if a reader views the source file, however.
Comments such as the name of the person updating a
file, the software and version used in creating a file,
or
the date that a minor edit was made are the norm..To
include a comment, enter:
<!-- your comments here -->
You must include the exclamation mark and the hyphens
as shown.
For More Information
This guide is only an introduction to HTML, not a comprehensive
reference. Below are additional online
sources of information. Remember to check a bookstore
near you for Web and HTML books.
Style Guides
The following offer advice on how to write "good"
HTML:
Composing Good HTML
W3C's style guide for online hypertext
Other Introductory Documents
These cover similar information as this guide:
How to Write HTML Files
Introduction to HTML
the Yale Center for Advanced Instructional Media pages
The HTML Quick Reference Guide, which provides a comprehensive
listing of HTML codes
Additional Online References
Official HTML specification
A description of SGML, the Standard Generalized Markup
Language
NCSA HTTPd server software information
Tables on the Web
Background images
Forms and the essential scripts explained
Java, snazzy stuff that is really perking up the Web
Thanks
A Beginner's Guide to HTML / revised May 2001
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