code: private Variable parseVariable(Node el) {
          Variable variable;
          if (nodeHasAttribute(el, TAG_VAR_ATTR_REGEX)) {
              variable = new Variable(
                      nodeAttribute(el, TAG_VAR_ATTR_NAME, Variable.DEFAULT_NAME),
                      java.util.regex.Pattern.compile(
                              nodeAttribute(el, TAG_VAR_ATTR_REGEX)
                      )
              );
          } else {
              variable = new Variable(nodeAttribute(el, TAG_VAR_ATTR_NAME, Variable.DEFAULT_NAME));
          }
          variable.setGhost(nodeAttribute(el, TAG_ATTR_GHOST, PatternElement.DEFAULT_GHOST_VALUE));
  
          if (nodeHasAttribute(el, TAG_VAR_ATTR_ACTION)) {
              variable.setAction(Action.valueOf(nodeAttribute(el, TAG_VAR_ATTR_ACTION)));
          }
          return variable;
      }
docs: Parse variable. The part of pattern.
  
  @param el DOM-element
  @return variable