The version number must have the form "X.Y.Z" where X, Y, and Z are non-negative integers, and must not contain leading zeroes. The description allows any content but should be limited to XHTML. A valid email address must follow several complex rules (see https://en.wikipedia.org/wiki/Email_address). For ROS packages only a few are enforced, and not the full character set is supported. The version limit must have the form "X.Y.Z", "X.Y", or "X". See documentation for VersionType for further details. Specified in REP 140 (see http://www.ros.org/reps/rep-0140.html). The package name should be unique within the ROS community. It may differ from the folder name into which it is checked out, but that is not recommended. It must start with a lower-case letter and consist of only lower-case letters, numbers and underscores. It must not have two consecutive underscores.