“与XSLT转换的处理器独立API”是什么意思？

I got this phrase in PHP manual page, but can't understand precisely.

Here is the link: http://www.php.net/manual/en/intro.xslt.php

What's the association between XSLT processor and XSLT library?

Each XSLT library implements or interfaces a given XSLT processor. All libraries (should) support a given minimum API regardless of what XSLT processor it implements. This minimum API is what is referred to in the documentation.