Please follow the suggestion, and add the new commit into #17298.

the modif timestamp should be read in "updateFromModelXml", but before calling it, as my comment shown: c64b81e#commitcomment-172744627

I don't understand why. And I have two reasons that I thought were pretty good for putting the check where I did:

First, That would mean I would have to have separate (duplicate/repeated) code in both getUserStylesFromXml() and getLangKeywordsFromXmlTree(), which would be doing the same thing (instead of doing the check where I put it, near the beginning of updateFromModelXml() before anything time consuming has been executed, and exiting the function early if the update doesn't need to happen, just like I do for the modelDate check after the model has been read). Alternately, I could create a new function that was called from both of the getXYZ functions (to avoid repeated code), but you had indicated earlier that you didn't want to create a new function.

Second, I would also have to then pass in the modif timestamp into the updateFromModelXml() so that I could postpone updating the XML-structure's value until after I've stored the "old version" for comparing, whereas if I read the modified timestamp inside the function, the string doesn't need to pass around from one function to another, because then it would only ever need to be used in the common updateFromModelXml().

Hmm... You're right about it.