# ally.is.focusRelevant

Determines if an element has any relevance to focus management.

# Description

This module is a pre-filter for ally.is.focusable, ally.is.tabbable, ally.is.onlyTabbable and ally.get.focusRedirectTarget. Elements may be considered focus-relevant, even though they do not in fact be focusable, tabbable, only-tabbable or redirect focus given their current conditions. But any element that is focusable, tabbable, only-tabbable or redirects focus is focus-relevant.

Consult the data tables what browsers consider focusable and what ally.js fails to consider focusable to learn how HTML elements behave.

# Usage

var element = document.getElementById('victim');
var isFocusRelevant = ally.is.focusRelevant(element);

# Arguments

Name	Type	Default	Description
element	`HTMLElement`	required	The Element to test.

The underlying rules can also be accessed in the options argument style by calling ally.is.focusRelevant.rules(options):

Name	Type	Default	Description
context	`<selector>`	required	The element to examine. The first element of a collection is used.
except	`<focus identification exception>`	`{}`	The Element to test.

# Returns

Boolean, true if the element is focus relevant.

# Throws

TypeError if element argument is not of type HTMLElement.

# Changes

Since v1.1.0 the <embed> and <keygen> elements are considered focus-relevant, but not focusable.
Since v1.1.0 the element.prototype.matches polyfill is re-applied to allow elements from other documents (e.g. from an iframe).
Since v1.1.0 the <object> element properly distinguishes between SVG and SWF content.
Since v1.1.0 elements using Flexbox layout are properly identified in IE10 and IE11.
Since v1.1.0 the ShadowDOM hosts are considered focus-relevant, but not focusable.
Since v1.1.0 scrollable containers are properly identified in Internet Explorer.
Since v1.1.0 all <area> elements are considered focus-relevant.
Since v1.1.0 every element that is either focusable, keyboard focusable, only tabbable or redirects focus is considered focus-relevant.
Since v1.1.0 exceptions can be passed to ally.is.focusRelevant.rules(options).
Since v1.1.0 IE9 properly resolves SVG links (<a xlink:href="…">).
In v1.3.0 the element.prototype.matches was replaced by util/element-matches.
Since v1.4.0 SVG elements with tabindex="-1" are handled properly in Firefox 51 (Bug 1302340) as well as MS Edge 14.
Since v1.4.0 only Blink considers <use … tabindex="-1"> focus relevant.
Since v1.4.0 only Blink and WebKit consider <foreignObject … tabindex="-1"> focus relevant.
Since v1.4.0 the document element (<svg>) of SVG documents in browsing contexts (<iframe>, <object>) is considered focus relevant in Firefox 51.

# Notes

The <body> element may mistakenly considered focusable, because it is the default activeElement if no other element has focus - but it is not focusable, unless made so by adding the tabindex attribute.

Because the <keygen> element is poorly supported, practically never used and has seen intent to deprecate, ally considers all <keygen> elements focus-relevant but not focusable.

Because the behavior of the <embed> element depends on the content type and browser plugin, ally considers all <embed> elements focus-relevant but not focusable.

Internet Explorer 9 supports VML (which was dropped in IE10 in favor of SVG), which allows linking using the href attribute. Ally.js does not understand VML because it does not exist in modern browsers anymore.

Firefox and Internet Explorer cannot focus SVGElements by script, thus no SVG element is considered focusable, see Gecko 1116966.

WebKit and Blink make any SVGElement focusable that has a focus event listener attached, see Blink 445798, WebKit 140024.

ally.is.focusable tests focus-relevant elements if they're also visible and not disabled
ally.is.tabbable tests elements if they're keyboard focusable
ally.is.validTabindex is used to verify the element's tabindex value is valid
ally.query.focusable finds focusable elements in the DOM
What Browsers Consider Focusable
What ally.js fails to consider focusable