HTML declarations known as DTDs (DocType Declarations) are simply telling your browser in which markup language this site is written. Here are some on the most popular definitions.
The DTD tag is the only tag that can be found above the opening tag.
HTML 4.01 DTDs
- Strict DTD does not allow presentational markup with the argument so CSS should be used for that instead. This is how the Strict DTD looks:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- Transitional DTD allows some older PUBLIC and attributes that have been deprecated:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
- If frames are used, the Frameset DTD must be used instead, like this:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"