[Commentor] LC-387 Bruno von Niman (ANEC W3C) on behalf of ANEC [Working Group decision] This is a specific best practice on use of "access keys" whose support is known to be quite uniform across mobile devices. We have added a clarification on the limitations of these accesskeys and the devices keyboards: "When building a list of links use numbered lists and assign access keys appropriately. It is recognized that not all characters can be used as access keys as many mobile devices have a limited keyboard." [Commentor reply] no reply from commenter [Comment] 
Chapter 5.2.6.1, What it means: This is a far more complex problem than just the limited keyboard (12-key keypads and soft-and hardware-based keyboards should be covered). In addition, aspects relating to the support, handling, mapping, sorting and transmitting characters should be addressed.