How is this construct `=function(argument)', `=scalar_name', `=scalar_value' etc. called, and where can I read more about it?

Nick Cox is putting to good use a construct which has same form like dereferencing of a local, except that inside there is no local but equal sign and sometimes a function, `=function(argument)', e.g.,

Code:

 
 . clear  . mat foo = [1,2,3,4,5]  . set obs `=colsof(foo)' number of observations (_N) was 0, now 5

or scalar name, two examples would be:

Code:

. sca Three = 3

. forvalues i = 1/`=Three' {
  2. dis `i'
  3. }
1
2
3

or

Code:

. clear

. set obs 4
number of observations (_N) was 0, now 4

. forvalues i=1/`=_N' {
  2. dis `i'
  3. }
1
2
3
4

From these examples I kind of see what this construct does, and I used it myself on a couple of occasions.

My question is, How is this construct described above called, and where in the Stata manuals I can read systematically regarding the rules according which this construct operates?

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