#TYPE FU CHROME HOW TO#
#TYPE FU CHROME FULL#

DevTools shows Chromium’s internal tree where roles and attributes tend to match those defined in the ARIA specification. PlatformsĮvery platform has a different accessibility API and while the shape of the tree is the same across all platforms, the API for interacting with the tree is different, and the names of attributes can differ. When designing the new tree view for DevTools, we have made some choices along the way about what part of Chromium’s accessibility internals we wanted to surface. In reality, there are quite a lot of different ways to experience the accessibility tree in Chromium. While this is true, we left out some complications in this description.

In the description of what the accessibility tree is you learned how Blink constructs an accessibility tree for the DOM it is rendering, and DevTools fetches this tree through CDP. In practice, the CDP backend listens for updates to the tree, keeps track of which nodes have been requested before, and sends events to the DevTools frontend if any of these nodes changes. It hooks into the same mechanics that would notify assistive technology of changes to the tree, and uses that to emit events to the DevTools frontend with updated nodes. The new tree view is live and dynamically updates if the accessibility tree changes in the renderer. Once a node is expanded in the tree, the children for the nodes are fetched through Chrome DevTools Protocol (CDP) and the tree is rebuilt. To make the tree performant even for larger sites, the tree is lazily constructed on the frontend as it is explored.

#TYPE FU CHROME FULL#

Now, when you toggle the new tree, it replaces the DOM tree view and allows you to see the full accessibility tree for the page: The previous tree view would only enable you to explore a single node and its ancestors. The following HTML document with a title, heading, and two buttons is used to show the tree. Now that you know how the accessibility tree works, you can use DevTools to see how the new tree view looks. We hope that the new tree will prove more explorable, useful, and easier to use. The new, full accessibility tree synchronized with the DOM tree so developers can switch back and forth between the two trees. Note: The HTML example was borrowed from here which also contains more information about how accessibility works in Chromium.

Since DevTools collects its accessibility information directly from the renderer process, this is the tree representation that DevTools handles. Still, most of these nodes only occur in the internal tree and would not be exposed to assistive technology. Note that this representation contains multiple superfluous nodes with role genericContainer, which seemingly contradicts the statement above that the accessibility tree is a simplified derivative of the DOM tree. Role='spinButton' editable focusable name='Age' value='42' role='rootWebArea' focusable name='How old are you?'

The renderer in Chromium, named Blink, derives an internal accessibility tree roughly as follows. Each node in the tree has a role such as Button or Heading, and often a name that can be either from ARIA attributes or derived from the node’s contents. Its structure is roughly the same, but simplified to remove nodes with no semantic content such as a element purely used for styling. The accessibility tree is a derivative of the DOM tree. Concretely, when a node is selected in the DOM tree viewer, the properties of the corresponding accessibility node displays in the pane together with a view of the node's ancestors and its immediate children.īefore we get to what this new full tree view looks like in DevTools, let us briefly go over what the accessibility tree is in more tangible terms. In Chrome DevTools, we provide the accessibility pane to help developers understand how their content is exposed to assistive technology. Web developers shape and manipulate the accessibility tree primarily through DOM properties such as ARIA attributes for HTML. The underlying model of this API is the accessibility tree: a tree of accessibility objects that assistive technology can query for attributes and properties and perform actions on.

#TYPE FU CHROME HOW TO#

In this post find out how this tree is created and how to use it in your work.Īssistive technology such as screen readers use Chromium’s accessibility API to interact with web content.

GitHub Note: Interested in helping improve DevTools? Sign up to participate in Google User Research here.Ĭhrome DevTools is launching a full accessibility tree making it easier for developers to get an overview of the whole tree.

Type fu chrome