6. The method of claim 4 , further comprising performing by the first thread: storing each new element in a data structure that stores a plurality of elements that currently exist in the document and an ID associated with each of the plurality of elements; and wherein the determining whether the element currently exists within the document that has the ID that is the same as the ID associated with the retrieved error checking result comprises determining whether the element is stored within the data structure that has the ID that is the same as the ID associated with the retrieved error checking result.
8. The method of claim 6 , wherein the storing each new element in the data structure comprises storing each new element in the data structure that stores a plurality of elements that currently exist in the document, an ID associated with each of the plurality of elements, and current position information associated with each of the plurality of elements; and wherein the generating the indication that the element is in error comprises obtaining from the data structure current position information associated with the element and generating the indication based on the current position information associated with the element.