Basically, the Document Object MODEL is a way of looking at a document. In that sense, it isn't all that different to CSS, which uses ANOTHER kind of mental model. CSS uses the IDEA of selectors to interact with a document. The DOM, on the other hand, views a document as a tree of nodes: element nodes, attribute nodes and text nodes. The DOM provides a vocabulary for targeting and manipulating those nodes.
If a PROGRAMMING language SUPPORTS the DOM then you can use that same vocabulary to address any kind of markup document.

Basically, the Document Object Model is a way of looking at a document. In that sense, it isn't all that different to CSS, which uses another kind of mental model. CSS uses the idea of selectors to interact with a document. The DOM, on the other hand, views a document as a tree of nodes: element nodes, attribute nodes and text nodes. The DOM provides a vocabulary for targeting and manipulating those nodes.
If a programming language supports the DOM then you can use that same vocabulary to address any kind of markup document.