HTML Data Types 
What you can and what you can't
Both browsers generally adhere to the rules regarding data types in the HTML 4.01 specification. The few exceptions are noted below:
URIs
URIs that contain any characters that are not letters or digits should be escaped. While both browsers usually handle the encoding automatically, it is a good idea to go ahead and do it in the HTML code itself. The most notable example is the tilde character often used for the URLs of user homepages, mostly a Unix tradition. Thus the URL http://www.foo.com/~john/ is invalid; it should be written as http://www.foo.com/%7ejohn/.
Colors
Netscape and Explorer recognize a few more color names than the sixteen
stated in the specification, but their use is strongly discouraged. Since
you can use the
hexadecimal notation for any color, it's recommended that you use this even
for the sixteen defined colors, since their names have come under attack for
their ambiguity quite often. If you're writing HTML for the 4.01 version browsers,
it's a good idea to put all color attributes in style
sheets.
Multilength
The Multilength data type is partially supported by both Netscape and Explorer. Implemented mainly in the colgroup and frameset elements, both browsers don't recognize the syntax n* for lengths, and only recognize a single asterisk, which is equivalent to 1* according to the specification.
Link Types
The only link type supported by both Netscape and Explorer is Stylesheet.
Both Netscape and Explorer support linked stylesheets with media attributes in standard screen mode and in print for all media types. Media types all, screen and print are specifically supported. Both browsers also recognize @import rules and stylesheets referenced in this manner are correctly rendered according to any media attribute in the referring document's link element.
Frame Target Names
The two browsers both interpret target attributes as window names and not frame names if a corresponding frame doesn't exist. This is exactly as stipulated in the specifications.
  
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