The syntax of NED files has changed significantly from the 3.x version. The NED editor primarily supports the new syntax. However, it is still possible to read and display NED files with the old syntax. It is important to note that many of the advanced features (syntax highlighting, content assistance, etc.) will not work with the old syntax. There is automatic conversion from the old syntax to the new, available both from the NED editor and as an external utility program (nedtool).

The gned program from OMNeT⁠+⁠+ 3.x viewed NED files in isolation. In contrast, the OMNeT⁠+⁠+ IDE gathers information from all .ned files in all open OMNeT⁠+⁠+ projects and makes this information available to the NED editor. This is necessary because OMNeT⁠+⁠+ 4.x modules may inherit parameters, visual appearance or even submodules and connections from other modules, so it is only possible to display a compound module correctly if all related NED definitions are available.