[DOC] regex breakdown for human parseble amount

src/js/ripple/amount.js

@@ -593,6 +593,21 @@ Amount.prototype.invert = function() {
  *   25.2 XRP    => 25200000/XRP
  *   USD 100.40  => 100.4/USD/?
  *   100         => 100000000/XRP
+ *
+ *
+ * The regular expression below matches above cases, broken down for better understanding:
+ *
+ * ^\s*                         // start with any amount of whitespace
+ * ([a-z]{3})?                  // optional any 3 letters
+ * \s*                          // any amount of whitespace
+ * (-)?                         // optional dash
+ * (\d+)                        // 1 or more digits
+ * (\.(\d*))?                   // optional . character with any amount of digits
+ * \s*                          // any amount of whitespace
+ * ([a-f0-9]{40}|[a-z0-9]{3})?  // optional 40 character hex string OR 3 letters
+ * \s*                          // any amount of whitespace
+ * $                            // end of string
+ *
  */
 Amount.human_RE = /^\s*([a-z]{3})?\s*(-)?(\d+)(\.(\d*))?\s*([a-f0-9]{40}|[a-z0-9]{3})?\s*$/i;