Highlight matching strings within text nodes that resulted from a ngram search. The function takes a sequence of nodes as first argument $nodes and a callback function (defined with util:function) as second parameter $function-reference. Each node in $nodes will be copied into a new document fragment. For each ngram match found while copying a node, the callback function in $function-reference will be called once. The callback function should take 2 arguments:

1) the matching text string as xs:string,

2) the node to which this text string belongs.

The callback function should return zero or more nodes, which will be inserted into the resulting node set at the place where the matching text sequence occurred.

Note: a ngram match on mixed content may span multiple nodes. In this case, the callback function is called once for every text node which is part of the matching text sequence.