The <
, =
, and >
characters (#x003C, #x003D, #x003E) are not allowed in attribute values declared as enumerated.
In an attribute declared to have enumerated values, the values must match Nmtoken
(one or more NameChar
s). That excludes several characters, including <
, =
, and >
, which are not part of the definition of NameChar
.
<
is especially troublesome (it is the start-of-tag delimiter in XML markup) and is not allowed in any attributes.