[whatwg] Request for implementer feedback: granularity definitions for Selection.modify()

Ian Hickson ian at hixie.ch
Sun Jan 30 15:18:10 PST 2011

On Sun, 30 Jan 2011, Aryeh Gregor wrote:
> I'm working on a definition of Selection.modify(), and have run into the 
> problem of how to define the various granularities used there. (See 
> <https://developer.mozilla.org/en/DOM/selection/modify> for basic docs.)  
> The intent of the API is clearly that, e.g., selection.modify("move", 
> "right", "character") should do something like hitting the right arrow 
> key, selection.modify("extend", "right", "line") should be like 
> Shift+Down, etc.  But this is platform-specific in practice -- e.g., 
> Ctrl+Left and Ctrl+Right use different definitions of word boundaries in 
> different programs I use.
> To what degree should I try to define how these granularities work?  I 
> could go ahead and say that moving by characters should be done by 
> moving to the next grapheme cluster boundary as defined by UAX#29, for 
> example.  Or I could say that it should follow platform conventions for 
> when the user advances by a character, e.g., using the right and left 
> arrow keys.  Or maybe something else?  What would implementers prefer?
> In practice, in other places where this stuff is needed (like 
> line-breaking or :first-letter), we just leave it entirely undefined, 
> which doesn't seem ideal but perhaps isn't fully avoidable.

I think leaving it undefined is fine so long as the behaviour is 
consistent, e.g. that the boundaries used for text-transform:capitalize 
match the boundaries used for word boundaries in Selection.modify(). This 
may need some coordination work so that the specs use terminology that is 
unambiguously referring to equivalent concepts, without precluding that 
Selection be implemented in non-CSS UAs.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
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