Textual criticism

It sounds like someone is complaining about the text. It's actually the process of comparing different copies in order to discover the original wording. It's very useful for everything from folios of Shakespeare, clay tablets about Gilgamesh, to parchments and codices of the Bible.

Some of  the rules a text critic follows:

• old manuscripts tend to be closer to the source
• briefer texts are more probable than longer ones because a scribe is more likely to add an explanation than subtract unless they deleted a controversial passage
• bad grammar and ugly writing are more likely to be original
• the writer's style is like their fingerprint and so critics can see interpolations by others

Text critics often compile an "eclectic edition" using a collection of various source documents and then others can use that for their own work in translation. There is an eclectic edition of Greek New Testament texts called the Nestle-Aland that many modern Bible translators consult. It contains notes on variants in the source documents and why one reading or interpretation was chosen over another.