Visibly Pushdown Languages (VPLs), recognized by Visibly Pushdown Automata (VPAs), are a nicely behaved family of context-free languages. It has been shown that VPAs are equivalent to Extended Document Type Definitions (EDTDs), and thus, they provide means for elegantly solving various problems on XML. One of the important problems about XML that can be addressed using VPAs is the validation problem in which we need to decide whether an XML document con- forms to the schema specification given by an EDTD. In this thesis, we are interested in solving the approximate version of this problem, which is to decide whether an XML document can be modified by a tolerable number of edit operations to yield a valid one with respect to a given EDTD. For this, we define Edit Visibly Pushdown Transducers (EVPTs) that give us the framework for solving this problem ([23]). We propose two algorithms; the first algorithm solves the approximate validation for any EDTD in PTIME. The second algorithm solves the same problem for an interesting subclass of EDTDs (those rec- ognizable by FSA) in constant space using only a single pass over the document.