(a) General rule.--A matter is commenced for the purposes of this chapter when a document embodying the matter is filed in an office authorized by section 5103 (relating to transfer of erroneously filed matters) or by any other provision of law to receive such document.
(b) Implementing court rules.--Subsection (a) may be made more specifically applicable to particular classes of matters, including interparty claims therein, by general rules further defining the document which when filed shall constitute the commencement of a matter.