[whatwg] Control over selection direction

[Marijn Haverbeke]

Hi,

I'd like to propose a minor addition to 4.10.20 APIs for the text
field selections. When programmatically setting the selection of a
text input, it is currently impossible to create a range with the
'anchor' at the bottom and the 'base' at the top. Concretely, this
means that, after a selection has been set by a program, if the user
presses shift and moves the cursor, it is always the bottom of the
selection that is moved. When doing heavy scripting on such input
element, it is often necessary to restore a previous selection exactly
as the user made it. This is currently not possible, and I'd say the
HTML5 standard is our only hope of finally getting something like this
widely implemented.

The most obvious way to handle this would be to allow selectionStart
to be greater than selectionEnd. This is, however, unacceptable for
various reasons -- it's not easily feature-detectable, it breaks older
code that reads these properties and expects start to never be greater
than end, and it makes the names more confusing than they have to be.

So I propose a selectionAnchor property, which holds either "top" or
"bottom", and can be set to one of these strings to modify the
direction. "top" would mean the anchor lies after the base of the
selection, so further shift-movement modifies the bottom, whereas
"botton" means the inverse, with movement modifying the top. (I think
the "top"/"bottom" terminology shouldn't break with any languages that
order characters differently. Does anyone write bottom to top? If
someone sees a problem, we could choose other terms, but these are the
most obvious I could come up with.)

So, in standard-ese:

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element.selectionAnchor [= value]

Returns either "top" or "bottom", indicating the side of the selection
that is anchored.

Can be set to change the side of the selection that counts as the anchor.

[...]

The selectionAnchor attribute must, on getting, return one of the
strings "top" or "bottom". "bottom" is returned when the anchor, the
fixed end, of the selection lies before the base, the movable end.
"top" is returned in all other cases.

When set to "top" when its current value is "bottom", or set to
"bottom" when its current value is "top", is must flip the roles of
the ends of the selection, so that what used to be the anchor now
becomes the base. When set to any other value, this is ignored.

------

Let me know what you think.

Best,
Marijn Haverbeke