An incremental parser for hierarchical files is provided where the file can be parsed into a tree representation. Changes to the file can effectuate incremental changes to the tree such that the whole hierarchical file need not be reparsed; the incremental change modifies the necessary portions of the tree, not necessarily the entire tree. Moreover, the incremental parser can intelligently handle errors related to modification of the hierarchical file, such as unmatched tags corresponding to unmatched nodes in the tree. Such error handling provides operability with the malformed hierarchical file rather than providing an error and/or rejecting the file as modified.