re: https://www.gnu.org/software/m4/manual/m4.html - UPDATE

[Howard Johnson]

OOPs.  Now I see that in fact the leading quote is a back tick (not a single tick), while the trailing quote is a single tick.  Strange. 

Might be good to spell this uncommon usage out more clearly in https://www.gnu.org/software/m4/manual/m4.html#Quoted-strings

i.e. say:

    A quoted string is a sequence of characters surrounded by quote strings, defaulting to ‘`’ (back tick) and ‘'’ (single quote), where the nested begin and end quotes within the string are balanced. The value of a string token is the text, with one level of quotes stripped off.

rather than just:

    A quoted string is a sequence of characters surrounded by quote strings, defaulting to ‘`’ and ‘'’, where the nested begin and end quotes within the string are balanced. The value of a string token is the text, with one level of quotes stripped off.