HTML entities are necessary in [attributes]! Otherwise it is not [valid HTML]. This violation most occurs as [ampersands] in [HREF] [URL]s; here are some reasons why you should avoid it:

[Appendix] Item B.2.2 of the [World Wide Web Consoritum|W3C]'s [HTML 4.0] specification explicitly tells you to.
Section 2.2 of [RFC 1738]: [Uniform Resource Locators] tells you to.
Section 4.4 of the W3C's [XML 1.0] specification tells you that not using entities in an attribute value is "Forbidden".
Any programs that parse using a [validating parser] will choke on unescaped character entities.
[XML] makes it clear that there is very little difference between attribute values and [character data] in a [XML tag|tag]. Therefore it should be possible to move [CDATA] from one to the other without additional parsing.
According to a discussion on the W3C's [www-html@w3.org|HTML mailing list] in February of 1998, the only known browser that doesn't parse HTML entities in attribute values correctly is [Amaya] 1.1c Beta.

Please, [for the children|for the sake of the children], use HTML entities in your attribute values.

HTML entity