Descriptions of Document Types come in three flavours (DTDs). The XHTML Transitional standard is the most user-friendly and widespread.
Below is a catalogue of XHTML Doctypes:
Very Restricted Baseline for Transitional Frameworks
You must use extreme caution while crafting XHTML documents due to the small number of XHTML elements and attributes that may be supported by one DTD but not by another. You should exercise caution while picking out XHTML components or attributes.
A Strict Document Type Definition for XHTML 1.0
Use it if you wish to avoid writing most of the XHTML properties and instead rely solely on the Cascading Style Sheet (CSS).
The following DTD should be included at the beginning of your XHTML file.
Syntax:
You may get the recommended XHTML 1.0 Strict document structure here:
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Strict//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd”>
DTD for the Transition to XHTML 1.0
If you need to use a lot of XHTML attributes but only a few CSS properties, you should use.
Make sure that your XHTML file begins with the following DTD.
Syntax:
The document type declaration for XHTML 1.0 Transitional is
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>
In the XHTML 1.0 Frameset Document Type Definition
If you wish to divide the browser window into multiple frames, you should utilise HTML Frames.
Make sure that your XHTML file begins with the following DTD.
Syntax:
Please use the following document type declaration:
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Frameset//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd”>
Keep in mind that it doesn’t matter whatever DTD you use to create your XHTML document; as long as it validates, your work will be accepted as high quality.