Importing one XSLT into another is very similar to including it. The only difference is that, when importing, templates defined in the importing XSLT take precedence over templates in the imported XSLT. In other words, if there are conflicting templates, the template in the imported XSLT is ignored.
The xsl:import element must be the first element after the open xsl:stylesheet tag. Here is an example of a document that imports HTML.xsl.