For More Information
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
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.
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.
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 = "ie_anima.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 = "ie_anima.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 = "ie_anima.gif">
</p>
which results in:
The image is centered; this paragraph starts below it
and left justified.
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.
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 browser
replicates it enough times to fill your window. This
action is automatic when you use the background tag shown
below.
The tag to include a background image is included in
the <BODY> statement as an attribute:
<BODY BACKGROUND="filename.gif">
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:
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">link
anchor</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.
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.
|
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. |
|
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.
|
The general format of a table looks like this:
<TABLE> <== start of table definition
<CAPTION> caption contents </CAPTION> <== caption definition
<TR> <== start of first row definition
<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.
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.
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.
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:
Other Introductory Documents
These cover similar information as this guide:
Additional Online References