Unique Ids?

Hi there,

in which scopes should ids be unique?

Our site has a lot of hierarchical ZMS-nodes (one on the top, about 50
subordinate nodes).
I think, within one node, all ids are unique, but not within the whole
tree. There are a lot of subnodes which are copied and pasted from one
sample which have nearly the same structure with same ids.

I ask, because we have a lot of troubles with ZMSLinkElements which
often suddenly break. It seems, there is a correlation when someone does
content work in some complete different area, but where ids are similar.

Regards
PeterZ, JKU