Lots or file formats are just zipped XML.
I was reverse engineering fucking around with the LBX file format for our Brother label printer’s software at work, because I wanted to generate labels programmatically, and they’re zipped XML too. Terrible format, LBX, really annoying to work with. The parser in Brother P-Touch Editor is really picky too. A string is 1 character longer or shorter than the length you defined in an attribute earlier in the XML? “I’ve never seen this file format in my life,” says P-Touch Editor.
Sounds like it’s actually using XSLT or some kind of content validation. Which to be honest sounds like a good practice.
Here’s an example of a text object taken from the XML, if you’re curious: https://clips.clb92.xyz/2024-09-08_22-27-04_gfxTWDQt13RMnTIS.png
EDIT: And with more complicated strings (like ones havingnumbers or symbols - just regular-ass ASCII symbols, mind you) there will be tens of <stringItem>, because apparently numbers and letters don’t even work the same. Even line breaks have their own <stringItem>. And if the number of these <stringItem> and their charLen don’t match what’s actually in pt:data, it won’t open the file.