about \underline markup command

[Gilles THIBAULT]

Reading the documentation pdf for Lilypond 2.11.36, i saw that a new markup 
command has been added : \underline.
I felt very happy ("Oh yes they did it !!!")
But ...

%%%
\version "2.11.37"
\markup { \underline "hello"}
{c'1}
%%%

=> Lilypond doen't recognize this command.

Is the documentation in advance?  So, does it really mean that this feature 
will come in a  near future release ?

Gilles