As an example: Build a (erroneous) valrep for a tree and assign this by $valrep to the tree-field Now issue a edit or show. One will see in the status line a message that something is wrong about the tree definition. But there is no feedback like a negativ $procerror or $status after edit/show. So it is immposible to catch such error by program code. What's needed is a forwarding of errors occurring implicit on executing a statement. BTW: an ONERROR statement would be a great help to catch such errors :-)
When ever a implicit error occurres, $procerror should set to a proper error number. Errors with higher severity should supersede previous errors (on executing the same statement)
It is impossible to for end user to report such kind of errors. The see some hints running through the status line but could'nt tell what exactly happend So it would be a good idea to be enabled to catch all this errors by progcode.