How to document an element?

[dv]

Hello,

I have been cleaning up the mpg123 element, and tried to add gtk-doc 
documentation to it. However, no generated HTML output for it is available.

I added this block to the beginning of the .c file:
/**
  * SECTION: element-mpg123audiodec
  * @see_also: lamemp3enc, mad
  *
  * Audio decoder for MPEG-1 layer 1/2/3 audio data.
  *
  * <refsect2>
  * <title>Example pipelines</title>
  * |[
  * gst-launch filesrc location=music.mp3 ! mpegaudioparse ! 
mpg123audiodec ! audioconvert ! audioresample ! autoaudiosink
  * ]| Decode and play the mp3 file
  * </refsect2>
  */

and added the header to EXTRA_HFILES in docs/plugins/Makefile.am , and 
ran autogen.sh afterwards. Still, no html file was generated for the 
element. What am I missing? I couldn't find anything about this topic in 
the documentation.