Word has compiler errors, and it even has bugs in its compiler sometimes (Word 2007 has one where it needed a character to show a table cell when that cell cont

Word has compiler errors, and it even has bugs in its compiler sometimes (Word 2007 has one where it needed a character to show a table cell when that cell contained nothing but a certain kind of image; this was fixed in Word 2010+ but not there). This is only really relevant if you're generating Word documents programatically from other data sources (it's very easy to do this with the MS-provided tools which can auto-generate code-behind for programs that need to make documents like this), but it's entirely possible to end up with invalid OOXML that means the document doesn't load. Some are recoverable, some aren't.