Select
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The Select tool is is a wrapper around LSelect, SSelect, VSelect and Blender's native loop select tool.
It allows you to access all four via a single keymap, which is intedend to be the same as Blender's own loop select keymap, which in turn may varry depending on your key config choice.
Always Loop Select
By default - and in Edge mode - connected sharps edges will be selected, if the entire edge selection consists of sharp edges, otherwise an angle based loop selection is done.
However, this behavior can be overriden, with the Always Loop Select option.
enforce loop selection, even with a selection of only sharp edges
This can be handy, if you are working on a mesh with a lot of sharp edges, and you still want to use Loop over Sharp selection, and avoid having to constantly toggle back into Loop selection mode.
Selection
Selection requirements are the same as for LSelect, SSelect and Vselect.
If they aren't met, Blender's native loop select will be called.