12. A non-transistory machine-readable medium tangibly embodying a program of machine-readable instructions executable by a digital processing apparatus to perform a method of editing a set of rules contained in a first document, said rules defining a transformation of data on a second document, said first document and said second document having elements constructed in a tree structure having nodes, each said rule on said first document having a template structure including at least one match condition, said match condition being an expression in said template that describes a subset of tree nodes, said method comprising: selecting at least one rule in said first document; checking a match condition of said at least one selected rule with said tree nodes from said second document to determine which structures in said scone document match said selected rule; presenting a listing of proposed rule modifications based on said determining of said matched structures in order to provide said edited set of rules, wherein said edited set of rules defines a transformation of said data on said second document to produce a resulting output document having a structure determined exclusively by said edited set of rules, and by the structure of said second document; and merging any rules having an identical effect into a single rule.
12. A non-transistory machine-readable medium tangibly embodying a program of machine-readable instructions executable by a digital processing apparatus to perform a method of editing a set of rules contained in a first document, said rules defining a transformation of data on a second document, said first document and said second document having elements constructed in a tree structure having nodes, each said rule on said first document having a template structure including at least one match condition, said match condition being an expression in said template that describes a subset of tree nodes, said method comprising: selecting at least one rule in said first document; checking a match condition of said at least one selected rule with said tree nodes from said second document to determine which structures in said scone document match said selected rule; presenting a listing of proposed rule modifications based on said determining of said matched structures in order to provide said edited set of rules, wherein said edited set of rules defines a transformation of said data on said second document to produce a resulting output document having a structure determined exclusively by said edited set of rules, and by the structure of said second document; and merging any rules having an identical effect into a single rule. 13. The non-transistory machine-readable medium of claim 12 , wherein said first document comprises an XSLT (eXtensible Style Language Transformations) stylesheet and said second document comprises an eXtensible Mark-up Language (XML) source data.