The tag_names_ns function fills the array arr with an alphabetical list of tags for the given document. If the namespace parameter is specified and not empty, then only those tags declared with that namespace URI are returned. If the namespace parameter is specified and is an empty string, then only those tags with no namespace are returned. If the namespace parameter is not specified, then all declared tags in the document type are returned, as well as tags in any foreign namespaces with the names qualified in the form {namespace-uri}local-name.

The function returns the number of entries loaded in the array.

The doc argument specifies the identifier of the document tree. If doc is omitted or 0, the current document is used.

This function is meant for XML documents. If doc refers to a non-XML document, the namespace parameter is ignored, and the function acts like tag_names(arr, 1, doc) was called.