[GeoNetwork-users] metadata edition : how to make appear an addLink (+) link for a metadata element or block ?

Hi,

I'm working on customizing a metadata template, based upon iso 19139, but
i'm having difficulties understanding how the add/remove Link mechanism
works. For some elements, even some i wouldn't want this possibility to be
offered, an addLink (+) corresponding buttons (x and up/down buttons) are
proposed. But for some element i would like this possibility to be offered,
i can't manage to make it appear.
Let's use an example. Let's create a new metadata from the Raster template
for iso 19139, and go to the Spatial representation info block. Suppose i
have a 4 dimensions raster. I would have 4 axis to document. The template
proposes only 3, but ideally, it should be possible to propose to the user
to add other ones.
And it is the same for Distribution info : how to add supplemental services
?
Of course, it is still possible through the xml view, but i want to be able
to do it through the form layout...

I found some erferences to addLink in metadata.xsl, but didn't manage to
figure out how it works... can someone give me some light ?
Thanks

Jean