C macros are indicated by the structured comment /*M ... M*/.
Unlike the case of C routines, macro definitions do not provide any
information on the types of the arguments.
Thus, the body of a structured comment
for a C macro
should include a synopsis section, containing a declaration of the
macro as if it were a C routine. For example, if the Add example were
implemented as a macro, the structured comment for it would look like
/*M Add - Add two valuesIt is important that the word Synopsis be used; bfort and related programs (doctext and doc2lt) use this name to find the C-like declaration for the macro.Parameters: . a1,a2 - Values to add
Synopsis: int Add( a1, a2 ) int a1, a2; M*/