There are two types of listings in a browser profile: supported tags and attributes, and supported tags with unsupported attributes. Unsupported tags automatically generate error messages and do not appear in the file.

A supported tag looks like this:

<!ELEMENT U name="Underline" >
<!ATTLIST U
>

A comment looks like this:

--Note: The closing angle bracket for an attribute list must appear on a line by itself. The two dashes denote comments in this kind of file.

This example uses the real-life <> tag. A (fictional) tag with unsupported attributes looks like this:

<!ELEMENT FOO Name="Foobar designator">
<!ATTLIST FOO
monkey !Error !msg="The monkey attribute of the FOO tag is not supported by Buckaroo Bonzai. Try using dork instead."
dork
geek ( STARTREK | MUD | MIDI )
nerd !Error !htmlmsg="<b>The nerd attribute of the FOO tag is not supported by Buckaroo Bonzai.</b>"
>

In this wholly fictional example, the FOO tag has the attributes monkey, dork, geek, and nerd, but only dork and geek are recognized by the Buckaroo Bonzai browser. If you simply left monkey and nerd off the list, they would automatically generate an error message when detected--but these are examples of custom error messages. The !htmlmsg designation allows you to use tags in the error message itself.

The geek attribute is an x = y attribute. The code for this tag could look like this:

<foo GEEK="startrek">