[OrangeRange]

When working in Java a couple of years ago I once ran into a random Prolog error. Turns out that the XML parser used by a large subset of the Java world is written in Prolog

(Hint: the error came from an Apache lib, just like in this link: https://stackoverflow.com/questions/3030903/content-is-not-a...)

[tannhaeuser]

Nope, that's a misunderstanding on your part I'm afraid. The "prolog" in that error message/SO question refers to an XML prolog, which is the part in an SGML/XML document up to the first content element ie. an XML declaration and a DTD, both optional.

[jodrellblank]

That's https://www.merriam-webster.com/dictionary/prologue - "the preface or introduction to a literary work".