Awesome Fetch API

Summary

A bulk data fetching API is designed to

to search the data through a web page
to retrieve portions of a web page in a single call

which allows to

decrease number of calls the AT has to poke into a server
create buffer-less screen readers
create lazy and lightweight server implementations

A typical scenarios are

Navigation: AT fetches next/prev heading while the user moves through a web page
Read a range: AT reads a paragraph by lines

Terms and concepts

Terms:

Search filters which allows to narrow the data that AT is interested in, for example, find all accessible having a heading role
Result specifiers which allows to specify what kind of data should be fetched, for example, AT is interested to retrieve accessible names and boundaries
AOM points (accessible object model aka DOM) which are used to identify and compare ranges in a document. Inspired by DOM point concept.

Also it operates with AT concepts, which are:

role - a primary characteristic of object like button
states - boolean characteristics of object like focused or selected
attributes - a named property having a scalar value (not boolean), for example level:1
relations - a named property pointing to other object such as label_for
boundaries - an object boundary in form of a rect
text - text

Proposal

Search

Search filters

Filter is a boolean expression consisting of conditions combined by boolean operators like: cond1 && cond2 || cond3, where condN is a boolean function which returns true for each accessible object complying a function's criteria.

Suggested boolean functions:

is(trait) - returns true if an accessible object has a given trait which may be role or state. For example is(listitem) && is(selected) indicates all selected list items.

has(property[, value]) - return true for an accessible object having a property of a value if provided, for example, has(level, 5) stands for all objects having level attribute with value of 5.

A value of has method is not necessary a scalar value. If a property points to an object, then a boolean function can be used as a value. For example, has(controls, is(listbox)) will return an object which controls a listbox object.

Search/Query API

Search/query is a way to find points or a range complying a search criteria.

query(AOMPoint anchor, String direction, String searchTerm, AOMPoint start, AOMPoint end)

to return a a first AOM point complying a search term.

queryAll(AOMPoint anchor, String direction, String searchTerm, AOMPoint start, AOMPoint end)

to return a list of all entries complying a search term.

Data fetching

Result specifiers

Results specifiers are used to scope fetched data. The format is property:value,[value,...]. For example role;states;attributes:level,xml-roles will return role, states, level and xml-roles attribute.

Data format

The fetching data is supposed to be in JSON format. For example,

[{
  role: "heading",
  states: [
    "invisible", "offscreen"
  ],
  attributes: {
    xml-roles: [ "super-button", "lower-button" ]
  },
  boundaries: [ x, y, width, height ],
  text: [
  ]
},
{
  role: "heading",
  states: [
    "visible", "onscreen"
  ],
  attributes: {
    level: 1
  },
  boundaries: [ x, y, width, height ]
}]

API

So used to fetch all

fetch(in AOMPoint start, in AOMPoint end, out String serializedRange)

returns a string of data of the above format.

Accessibility/Awesome Fetch API

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