Reimplement PL's default listitems feature with the mustache syntax

Author: dnwhte

packages/patternengine-node-nunjucks/README.md

@@ -4,7 +4,7 @@
 
 To install the Nunjucks engine in your edition, `npm install patternengine-node-nunjucks` should do the trick.
 
-Level of Support is more or less full. Partial calls and lineage hunting are supported. Nunjucks does not support the mustache-specific syntax extensions, style modifiers and pattern parameters, because their use cases are addressed by the core Nunjucks feature set. Pattern Lab's listitems.json data does not appear to be accessible. However, it's still possible to create custom list style data.
+Level of Support is more or less full. Partial calls and lineage hunting are supported. Nunjucks does not support the mustache-specific syntax extensions, style modifiers and pattern parameters, because their use cases are addressed by the core Nunjucks feature set. Pattern Lab's listitems feature is still written in the mustache syntax.
 
 ## Extending the Nunjucks instance
 

packages/patternengine-node-nunjucks/lib/engine_nunjucks.js

@@ -13,8 +13,8 @@
  * Nunjucks does not support the mustache-specific syntax
  * extensions, style modifiers and pattern parameters, because
  * their use cases are addressed by the core Nunjucks feature set.
- * Pattern Lab's listitems.json data does not appear to be accessible.
- * However, it's still possible to create custom list style data.
+ * Pattern Lab's listitems feature is still written in the
+ * mustache syntax.
  *
  */
 
@@ -68,6 +68,7 @@ var engine_nunjucks = {
   // regexes, stored here so they're only compiled once
   findPartialsRE: /{%\s*(?:extends|include|import|from)\s+(?:.*)\s*%}/g,
   findPartialKeyRE: /{%\s*(?:extends|include|import|from)\s+('[^']+'|"[^"]+")/,
+  findListItemsRE: /({{#( )?)(list(I|i)tems.)(one|two|three|four|five|six|seven|eight|nine|ten|eleven|twelve|thirteen|fourteen|fifteen|sixteen|seventeen|eighteen|nineteen|twenty)( )?}}/g,
 
   // render it
   renderPattern: function renderPattern(pattern, data) {
@@ -136,9 +137,10 @@ var engine_nunjucks = {
     }
   },
 
-  // handled by nunjucks. This is error to keep PL from erroring
+  // still requires the mustache syntax because of the way PL handles lists
   findListItems: function (pattern) {
-    return null;
+    var matches = pattern.template.match(this.findListItemsRE);
+    return matches;
   },
 
   // handled by nunjucks. This is error to keep PL from erroring