Adding warnings for non-standard escape sequence usage

src/js/parser/javascript/charset.js

@@ -41,5 +41,9 @@ export default {
     this.elements = _.unique(this.properties.parts.elements, part => {
       return [part.type, part.textValue].join(':');
     });
+
+    if (this.textValue.match(/\\c[^a-zA-Z]/)) {
+      this.state.warnings.push(`The character set "${this.textValue}" contains the \\c escape followed by a character other than A-Z. This can lead to different behavior depending on browser. The representation here is the most common interpretation.`);
+    }
   }
-};
+}