suggest check whitspace in attributes

[kryde]

The HTML 4 spec under "6.2 SGML basic types" says

User agents may ignore leading and trailing white space in CDATA
attribute values (e.g., "   myval   " may be interpreted as
"myval"). Authors should not declare attribute values with leading
or trailing white space.

As an idea for a feature, HTML::Lint might report attribute values with leading or trailing whitespace, so that for example href=" foo.html " is reported as something like: HTML4 says don't use leading or trailing whitespace (even if it often works).