Using a comment is awkward and unnecessary. If you have a very long function, you generally don't want to retrieve the full function later, while programming. Hence use the
usage option, which will retrieve merely the usage information you've entered:
generateXY::usage = "generateXY[e_, yvar_, extraDims_, dsize_] here e controls how correlated, ...";
Later, you mere type
to get the description, not all the (needless) code.
f[x_] := x^3; f::usage = "f[x] gives the cube of x"
? f f[x] gives the cube of x
retrieves the full information, should you need it:
f[x_] := x^3; f[x] gives the cube of x