package org.intellij.lang.jflex.fileTypes;

import com.intellij.openapi.fileTypes.FileTypeConsumer;
import com.intellij.openapi.fileTypes.FileTypeFactory;
import org.jetbrains.annotations.NotNull;

/**
 * JFlex file type factory, tells IDEA about new file type
 *
 * @author Jan Dolecek
 */
public final class JFlexFileTypeFactory extends FileTypeFactory {
    @Override
    public void createFileTypes(@NotNull FileTypeConsumer consumer) {
        consumer.consume(JFlexFileType.FILE_TYPE, JFlexFileType.DEFAULT_EXTENSION);
    }
}

@@ -502,39 +502,20 @@
 PE, 
-JFlexFileType.DEFAULT_EXTENSION
+%22flex;jflex%22
 );%0D%0A

Add .jflex as a supported file extension (in addition to .flex).