title_body: what does the v5.0 in the name of an e-book file stand for? I have seen various e-books on the Internet that have a (v5.0) in the name e.g. 
  
  Charles Darwin - On the Origin of Species (v5.0).epub
  
  
  Initially I thought this had to with the version 5 of the DocBook, but I have seen other versions (v3.4) that do not have a corresponding DocBook version.
  I have also seen this for e-books in .html and .txt files. Nothing in the those or the .epub file points at DocBook in any way.
  
  What does this (v5.0) stand for?
upvoted_answer: This is an indication of the quality of the ebook. (v5.0)  should be
  close to retail quality:
  
  v1.x: publication has been scanned and OCR-ed, but not spell checked.
  v2.x: publication has been scanned, OCR-ed, and spell checked but not proofread.
  v3.x: publication has been scanned, OCR-ed, spell checked, and proofread.
  V4.x: publication has been proofread by multiple persons and is near retail quality.
  v5.x: publication is of retail quality.
  
  
  Minor version numbers are normally used for committed/uploaded changes.
  
  I have not come across any (semi-)official website for these indications. I pulled these from my notes that I made while doing book scans myself. I think they came from some Usenet post. 
  
  Some v5 material still has a lot of errors (especially older publications where the fonts are not easily recognised by the OCR).