This is a complete list of the Syntax Errors recognized by the Consistency Checker. Elements that are part of a Syntax Error are highlighted in red color .
There are Syntax Errors for the following categories:
Edges connect shapes of the same type or an edge has an unconnected end.
Note: Please attach start/end point of edges to the connection points of shapes in order to recognize the connection. You can add as many edges to one connection point as you want.
Block Diagram: 

Petri Net: 

E/R Diagram: 

Edges must literally touch the shapes they are connected to, although they are snapped at the connection points.
Note: Please attach start/end point of edges to the connection points of shapes in order to recognize the connection. You can add as many edges to one connection point as you want.
Block Diagram: 
Petri Net: 
E/R Diagram: 
Depending on the diagram type or edge type, not all possible directions for an edge are allowed. Possible directions are directed (in either direction), bidirectional (arrows at both ends) or undirected (no arrows). Bidirectional edges are not allowed in any FMC diagram type.
Block Diagram: Generally directed and undirected edges are allowed. The two edges of a modfiying access can only be directed. 

Petri Net: Edges are always directed. 

E/R Diagram: Edges are always undirected. 

Nested shapes are allowed but the inner shapes cannot be connected to the outer shapes.
Block Diagram: 
Petri Net: 
E/R Diagram: 
The marking of a place cannot be higher than its capacity.
For a correct recursion, there must be at least two stack places, each of them with an edge to a transition that has an incoming edge from the same return place.