In order to deal with the perceived lack of standards with HTML, XML was designed from get-go to be intolerant of errors. We can see how this XML "precision decision" plays out when after one mistake in the document.xml file where all the text is stored within the larger docx zip structure, Microsoft Word will not display any text. This can be quite frustrating in a data recovery situation where partial recovery is better than nothing.
Quick Word Recovery attempts to fix document.xml files by identifying the first error and then truncating it 50 characters before. The extra truncation is sometimes needed because the XML validation often indicates an error only after several characters of bad XML have already been passed.
After truncation the program uses xmllint's recover command to add the correct xml ending tags and the file is rezipped and opened as a docx file in Word. File truncation length is configurable.