Guideline A.4.1: (For the authoring tool user interface) Help authors avoid and correct mistakes. [Implementing A.4.1] Rationale: Some authors with disabilities may be more susceptible to input errors due to factors such as difficulty making fine movements and speech recognition system errors. A.4.1.1 Content Changes Reversible (Minimum): All authoring actions are either reversible or the authoring tool requires author confirmation to proceed. (Level A) Implementing A.4.1.1 A.4.1.2 Settings Change Confirmation: If the authoring tool provides mechanisms for changing authoring tool user interface settings, then those mechanisms can reverse the setting changes, or the authoring tool requires author confirmation to proceed. (Level A) Implementing A.4.1.2 A.4.1.3 Content Changes Reversible (Enhanced): Authors can sequentially reverse a series of reversible authoring actions. (Level AAA) Note: It is acceptable to clear the authoring action history at the end of authoring sessions. Implementing A.4.1.3