Fixes to wording of 1.3.4 Purpose of Controls

These are completely optional suggestions, but address real errors in the current Editor's Draft's wording of 1.3.4 Purpose of Controls.

1. Since the draft wording that applies to the broad category of "user interface components" rather than just controls, the title should change from "Purpose of Controls" to something more general. For example, the title "Standard Purpose" would also help distinguish 1.3.4, about exposing purpose using a fixed vocabulary, from 2.4.4 Link Purpose (In Context), about exposing human-readable, free-form text.

2. The new wording introduced a grammatical error: in "In content implemented using markup languages, user interface components that serve a purpose identified in Appendix B can be programmatically determined" the object of "can be programmatically determined" is the *components*, but it should be those components' *purposes*. (It also mixes singular and plural, but that's done in some other SC.)

There are many constructions that would fix the latter problem; here are a few, and one can tweak them and mix-and-match specific wording choices:

     A. "When a user interface component is implemented using markup language and serves a purpose corresponding to one listed in Appendix B, that purpose can be programmatically determined."

     B. "In content implemented using markup languages, when user interface components serve purposes identified in Appendix B those purposes can be programmatically determined."

     C. "In content implemented using markup languages, for each user interface component that serves a purpose identified in Appendix B, that purpose can be programmatically determined."

     D. "For all user interface components implemented in markup languages, its purpose can be programmatically determined when that purpose corresponds to one identified in Appendix B."

     E. "For each user interface component implemented in markup languages, its purpose can be programmatically determined when that purpose corresponds to one identified in Appendix B."

     F. "The purpose of a user interface component can be programmatically determined when the component is implemented in markup language and its purpose corresponds with one identified in Appendix B."

     G. "The purposes of user interface components can be programmatically determined when those components are implemented in markup language and their purposes corresponds with ones listed in Appendix B."

     Greg