Searching the default key-bindings to find the equivalent of Ctrl-A and Delete:
When working with the ST-API it is easy to forget that often the simplest way is just to run a command.
To do this with the API:
some_view.erase(edit, sublime.Region(0, some_view.size())
FYI The content of a view can be considered the region (0, view.size()). This does not correspond directly to the number of (single) character-positions as the Tab character, which might cover e.g. four-space, can be regarded as a single character. Internally, it is a little more detailed than this suggests, because ST is able to extract from a region the line (row) and column positions. It must, therefore, (I'm guessing!) maintain an internal map of how different regions correspond to different *areas *of the view.
RegionSets are far less useful (than Regions) as we cannot arbitrarily create these. The most significant RegionSet is sel(), which we can clear and add-to, etc.. However, we can store Regions in a list which, effectively, can then behave like a RegionSet.