origin of `notation'

[Buchs, Kevin]

Ok, dumb question to which I have been unable to find the answer and which is 
distracting me: 

In emacs documentation, what is the origin of using the accent grave (backtick) 
to introduce a quoted phrase, often a command, while using an apostrophe to 
terminate it.  Example: (info) Keys and Commands: 1st paragraph: "binding" is 
quoted as such, but 2nd paragraph, `next-line' is quoted that way. If someone 
who knows the answer will take the time to answer, I promise I will document it 
on the Emacs wiki. Does this extend beyond emacs? Beyond GNU & FSF?

Kevin Buchs   |  Senior Engineer  |  Department of Physiology and Biomedical 
Engineering - SPPDG
507-538-5459  |   buchs.kevin@mayo.edu  |  http://www.mayo.edu/sppdg
Mayo Clinic  |  200 1st St. SW  |  Rochester, MN 55905