Added comments

lib/engine.js

@@ -5,21 +5,24 @@ module.exports = function(cssString) {
   var cssObject = css.parse(cssString);
   var longPropertiesPositions = [];
 
+  // Loop through every rule of the stylesheet
   cssObject.stylesheet.rules.forEach(function(rule) {
-    if (rule.type === "rule") {
+    if (rule.type === "rule") { // Exclude comments and other things that aren't rules
       var declarations = [];
 
+      // Create an array of the rule's declarations indexed by their property name
       rule.declarations.forEach(function(declaration) {
         declarations[declaration.property] = declaration;
       });
 
+      // Loop through all of the shorthandable properties to find if the current one can be shortened
       shorthands.forEach(function(shorthand) {
-        var shorthandValue = shorthand.getShorthandValue(shorthand, declarations);
+        var shorthandValue = shorthand.getShorthandValue(shorthand, declarations); // Defined in properties.js
 
-        if (shorthandValue !== "") {
+        if (shorthandValue !== "") { // If there are no the specific properties of the shorthand, "getShorthandValue" returns an empty string
           var newDeclarations = [];
 
-          // Add the new shorthand property
+          // Add the new shorthanded property
           newDeclarations.push({
             type: 'declaration',
             property: shorthand.shorthandProperty,
@@ -36,6 +39,7 @@ module.exports = function(cssString) {
             }
           });
 
+          // Replace the rule's old declarations with the new shorthanded ones
           rule.declarations = newDeclarations;
         }
       });