solo che ora non ho capito che cosa non va qua:

Warning Line 6 column 253: character "<" is the first character of a delimiter but occurred as data.

This message may appear in several cases:

You tried to include the "<" character in your page: you should escape it as "&lt;"
You used an unescaped ampersand "&": this may be valid in some contexts, but it is recommended to use "&amp;", which is always safe.
Another possibility is that you forgot to close quotes in a previous tag.