XSLT transformations accept a document tree as input and produce a tree as output. From the XSLT point of view, documents are trees built of nodes. XSLT recognizes seven types of nodes XSLT; here are those nodes, along with how XSLT processors treat them:
The document root— This is the very start of the document.
Attribute— This node holds the value of an attribute after entity references have been expanded and surrounding whitespace has been trimmed.
Comment— This node holds the text of a comment, not including <!-- and -->.
Element— This node consists of all character data in the element, including character data in any of the children of the element.
Namespace— This node holds the namespace's URI.
Processing instruction ...