Highlighted Text

[Dale M Petersen]

I am using Notepad++ 6.6.9 with the xlm language. When text is highlighted in blue, does that mean it should not be used? Therefore the highlighted text should be deleted. e.g. {-//W3C//DTD XHTML 1.0 Transitional//EN"} is highlighted and the w3 validation does not seem to like the (")
Is there location where definitions for why certain text are red and why text are highlighted.
Thank you for your help.