You may use the field «Remaining URL» to add URL-parameters like ?eventcategory=4.
I would also recommend the use of Remaining URL field. That will save your efforts.
In addition to suggetion by @Thomas you can also use it like
?category=yourcategoryname1&category=yourcategoryname2 for same category or for multiple categories
Thanks Tomas and Praful,
i have verified that this approach works, i like it. Just i'm still waiting for the ok of the customer. Maybe he finds this approach too complicated for the cms editors, they need to know that the Event-Category information must be appended as Url Parameter. So i've hoped for an easier way to customize the link-editor. I guess you can do it with a dojo widget, can't you? I'm just not very familiar with it and have hoped that someone could show this approach.
So i see that your way with using the "Remaining Url" is pretty straightforward and also easy to extend.
our customer wants the possibility to add a new property "Event-Category" to a link which we can use when the link is rendered.
Does the Link-Editor Dialog support custom elements?