Comment: "variations in presentation of text can be programmatically determined." - yes, a graphical browser can display italicised text, but not much, if any, AT can determine its existance.
reconsider/clarify/strengthen this SC, or drop the last part.
SC 1.3.1 and 1.3.4 have been combined to read "Information and relationships conveyed through presentation can be programmatically determined or are available in text, and notification of changes to these is available to user agents, including assistive technologies." This wording ensures that it is the meaning conveyed by the presentation that must be programmatically determined, and allows the author to indicate the meaning in text if it is not feasible to do so programmatically. The How to Meet document describes this in some detail.
Currently, many assistive technologies can determine the existence of variations in presentation, albeit with minimal usability. It is the information conveyed that is required by this success criterion. The information needs to be conveyed in a usable manner.