Documentation of music functions

[Carl D. Sorensen]

In the NR 6.3.3. and 6.3.4., there are nice examples of building a music
function.  The music functions are documented with standard Scheme doc
strings:

funcName =
#(define-music-function (parser location var-list) (var-types?)
  "This is the doc string for the function."
   return-value)

In ly/music-function-init.ly, the music functions are documented
differently:

funcName =
#(define-music-function (parser location var-list) (var-types?)
  (_i "This is the doc string for the function.")
   return-value)

What is the difference between these two syntaxes, and which should I use to
add doc-strings to addChordShape, storePredefinedDiagram, pointAndClickOn,
and pointAndClickOff, which are predefineds I created?

Thanks,

Carl