Add polling for selection changes on mobile devices

[JamesMGreene]

Start on:

• touchend
• window.onfocus

Clear on:

• touchstart
• touchcancel
• window.onblur
• when there is no longer any selection.

Initial idea from @JasonMore:
http://stackoverflow.com/questions/11300590/how-to-captured-selected-text-range-in-ios-after-text-selection-expansion

[JamesMGreene]

In addition to helping with mobile browsers, [configurable] polling should be considered for milestone Release 1.0 to bridge the gap on the various other trigger conditions for the textual select event.

See:

• select (and on MSDN
• selectionchange (and on MSDN
• Should be irrelevant to this functionality but including for posterity: selectstart (and on MSDN