* 仕様書

[REFS[
- [7] [CITE@en-US-x-hixie[HTML Standard]] ([TIME[2014-02-19 22:39:17 +09:00]] 版) <https://www.whatwg.org/specs/web-apps/current-work/#focus>
]REFS]

* フォーカス可能領域の順序

[6] [[フォーカス可能領域]]の順序は、[[木順]]ですが、[[DOM錨]]が同じである領域同士の[[順序]]は、
対応する[[CSS箱]]の[RUBYB[[[行きがけ順]]]@en[pre-order]]の[[深さ優先探索]]によって決まります [SRC[>>7]]。

[8] [[focusing steps]] における[[フォーカス可能領域]]の選択でも、
同様に対応する[[CSS箱]]の[RUBYB[[[行きがけ順]]]@en[pre-order]]の[[深さ優先探索]]が行われます [SRC[>>7]]。

* 歴史

[REFS[
- [1] [CITE@en[Web Applications 1.0 r8478     Revamp how focus is defined, to actually handle things we've ignored before, like viewports and scrollable regions]] ([TIME[2014-02-20 07:39:00 +09:00]] 版) <http://html5.org/tools/web-apps-tracker?from=8477&to=8478>
]REFS]

[2] >>1 によってそれまでの[[形容詞]]「[DFN[[RUBYB[[[フォーカス可能]]]@en[focusable]]]]」の定義はなくなり、
相当するものは[[名詞]]「[[フォーカス可能領域]]」に変わりました。

[FIG(quote)[
[FIGCAPTION[
[3] [CITE@en[XHTML™ 2.0 - Terms and Definitions]]
([TIME[2010-12-17 00:44:37 +09:00]] 版)
<http://www.w3.org/TR/2010/NOTE-xhtml2-20101216/terms.html#focusable>
]FIGCAPTION]

> focusable
> Elements are considered "focusable" if they are visible (e.g., have the equivalent of the '''['''CSS2''']''' property of "display" with a value other than none) not disabled (see '''['''XFORMS''']'''), and either 1) have an @href attribute or 2) are considered a form control as defined in '''['''XFORMS''']'''.

]FIG]


[4] [CITE@en[Note how the SVG that is actually implemented is a mix of SVG 1.1 and SVG Tiny 1.2 · Issue #126 · whatwg/html]]
([TIME[2015-11-18 11:30:28 +09:00]] 版)
<https://github.com/whatwg/html/issues/126>

[5] [CITE@en[Clarify and add some examples around focus]]
([[domenic]]著, [TIME[2016-11-03 04:45:57 +09:00]])
<https://github.com/whatwg/html/commit/deb83668390151a2cf242c24dd9d68509860e77a>