drools-eclipse/org.drools.eclipse/src/main/java/org/drools/eclipse/dsl/editor/DSLAdapter.java
private void loadConfig(IFile input) {
        IResource res = findDSLResource( input, dslConfigName );
        if (res instanceof IFile) {
            IFile dslConf = (IFile) res;
            if (dslConf.exists()) {
                InputStream stream = null;
                try {
                    stream = dslConf.getContents();
                    readConfig( stream );
                    valid = true;
                } catch ( Exception e ) {
                    throw new IllegalStateException("Unable to open DSL config file. (Exception: " + e.getMessage() + ")");
                } finally {
                    closeStream( stream );
                }
                
            }
        }
    }
private void loadConfig(IFile input) {
        IResource res = findDSLResource( input, dslConfigName );
        if (res instanceof IFile) {
            IFile dslConf = (IFile) res;
            if (dslConf.exists()) {
                InputStream stream = null;
                try {
                    stream = dslConf.getContents();
                    readConfig( stream );
                    valid = true;
                } catch ( Exception e ) {
                    throw new IllegalStateException("Unable to open DSL config file. (Exception: " + e.getMessage() + ")");
                } finally {
                    closeStream( stream );
                }
                
            }
        }
    }
This does the hunting around the projec to find the .dsl file.