--- /dev/null
+'use strict';
+
+module.exports = factory;
+
+/* Factory to de-escape a value, based on a list at `key`
+ * in `ctx`. */
+function factory(ctx, key) {
+ return unescape;
+
+ /* De-escape a string using the expression at `key`
+ * in `ctx`. */
+ function unescape(value) {
+ var prev = 0;
+ var index = value.indexOf('\\');
+ var escape = ctx[key];
+ var queue = [];
+ var character;
+
+ while (index !== -1) {
+ queue.push(value.slice(prev, index));
+ prev = index + 1;
+ character = value.charAt(prev);
+
+ /* If the following character is not a valid escape,
+ * add the slash. */
+ if (!character || escape.indexOf(character) === -1) {
+ queue.push('\\');
+ }
+
+ index = value.indexOf('\\', prev);
+ }
+
+ queue.push(value.slice(prev));
+
+ return queue.join('');
+ }
+}