Referenzen to meta data of other sites

[thmarx]

Sometimes the usage of other sites meta data would be helpful. I think some template function and content tag for that should be provided by the core cms.

Cms.node(link_to_node).meta or something like that.

[thmarx]

the PR constains an implementation using the template function feature of the tempate engine.

still need to check if editing hidden pages is possible in the manager.

[thmarx]

Pages in an hidden folder can not be edited in manager, because resolving the content in preview will not work. We should not fix that because it may introduce security issues.

[thmarx]

after sleeping about that issue, I think making the hidden files editable is totally necessary because people want to create 404 pages. so we make the hidden node visible, but online in Preview in Manager mode.