[whatwg] web-apps: API for text field selections is lacking

[Mikko Rantalainen]

The section

5.6.2. APIs for the text field selections
http://www.whatwg.org/specs/web-apps/current-work/#textFieldSelection

defines attributes selectionStart and selectionEnd and method
setSelectionRange().

These features are enough to identify the selected data and possibly
modify the contents of text field by scripting so that the modification
is affected by selected region.

There're some problems, though. I represent the following use case:

A page contains a textarea. Author adds an additional button for adding
a pair of parenthesis around the selected text. The javascript code for
this feature (given that "e" is the text field element) is

e.value = e.value.substr(0,e.selectionStart) + "(" +
e.value.substr(e.selectionStart,e.selectionEnd) + ")" +
e.value.substr(e.selectionEnd);

The problems with the above code:

1) From the UA view, the entire contents of the field has been replaced
with a new value and therefore the undo feature of the field cannot
represent the fact that the script only added character "(" before the
selection and character ")" after the selection. A method to update only
the selected part of the value would be needed to correctly describe the
real change to the value to the UA.

2) There's no good way to set the selection because if the scripts calls
 setSelectionRange() the UA "must set the selection of the text field"
but it is not required to modify the focus or scrolled part of the text
field in any way. In addition, there's no way to query the scroll
position of the selection so the script cannot work around this issue
either. As a result, setSelectionRange() may be used to set the
selection but the selected selection may end up being out of the view
from the user point of view. As textarea element may have soft wrapping
enabled, the script has no way to even compute the correct line number
for the selection start.

For the issue 1) I suggest adding a new method
	replaceSelectionText(in string selection_value)
which replaces the section of field's value between offsets
selectionStart and selectionEnd with the string selection_value. This
replacement should not destroy the text field's undo history - instead
it should be treated similarly to paste (text) operation.

For the issue 2) I suggest changing the behavior of setSelectionRange()
to require that the selection must be made visible to the user. Perhaps
something along the lines "UA must scroll the text field so that the
start of the selection is visible." As an alternative, a method such as
void focusSelection() could be added so that the script may hint the UA
that the selection should be made visible after the script has called
setSelectionRange() and replaceSelectionText() multiple times (so that
these actions do not repeatedly scroll the text field's viewport).

-- 
Mikko

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