The element is in the call‐for‐implementation phase.
+ +Usually, using the element is safe. However, it is a new feature + so that it might not be implemented correctly. If it is found that + the feature is hard or impossible to implement, the feature + might be revised, or in some case it might be dropped.
+ +Elements defined by HTML4, Atom 1.0, and XBL 2.0 belong to this + class.
+The element is in the last call‐for‐comments phase.
+ +The element is relatively mature, though the standardization + is not done yet. It may be used for experiments. Since it is a new + feature, it might not be implemented correctly or at all. If it is + found that the feature is hard or impossible to implement, the feature + might be revised or might be dropped.
+ +Elements defined by Web Forms 2.0 as well as some elements + defined by HTML5 belong to this class.
+The element is documented in a working or editor's draft + and not yet completed.
+ +The element should not be used for any practical purpose. + The feature might be drastically changed later or might be + entirely removed.
+ +Most of new elements defined by HTML5 belong to this class.
+The element is not part of any standard or draft.
+ +The element should not be used for any practical purpose.
+