Can you write up a little bit about what this is and how to use it? We will also need an issue to track getting support into clients, or else it is not usable.

@imurchie I can also create PRs for java_client (and, probably, for ruby and python clients as well). The only thing I don't like there is C# }:-)

This description can also be found at https://github.com/facebook/WebDriverAgent/wiki/Queries

The class chain query type is similar to xpath, but can only include indexes and valid class names. Only search by direct children elements of the current element is supported. Examples of such requests:
XCUIElementTypeWindow/XCUIElementTypeButton[3] - select the third child button of the first child window element
XCUIElementTypeWindow - select all the children windows
XCUIElementTypeWindow[2] - select the second child window in the hierarchy. Indexing starts at 1
XCUIElementTypeWindow/XCUIElementTypeAny[3] - select the third child (of any type) of the first child window
XCUIElementTypeWindow[2]/XCUIElementTypeAny - select all the children of the second child window
XCUIElementTypeWindow[2]/XCUIElementTypeAny[-2] - select the second last child of the second child window
One may use '*' (star) character to substitute the universal 'XCUIElementTypeAny' class name

This query type has been added as a quick patch to speed up complicated xpath queries containing many levels of nested nodes and not containing xpath function calls or attributes comparison (such locators are not recommended at all, but people still use them though)

OR

to combine them with predicate search, since location by predicates does not respect nodes hierarchy. For example:

The xpath locator

//XCUIElementTypeTable/XCUIElementTypeCell[@value='bla']

might be times slower than
class chain

XCUIElementTypeWindow/*/*/XCUIElementTypeTable[2]

and then apply predicate search to the previous result:

type == 'XCUIElementTypeCell' AND value == 'bla'

Sounds good. Once we have client implementations we'll need to add real documentation on its usage somewhere.

@imurchie Just let me know where to add ;)

I'll have to think about it! But it is not necessary until we have ways of sending in the query.

great work on getting a faster xpath-like query into WDA, @mykola-mokhnach

Thanks @jlipps. Also a nice piece of experience for me. It was literally implemented for the whole chain starting from WDA (ObjC) to Appium Server (NodeJS) and then Appium Java Client (java). There are also plans to do it for Python client when I have time and mood.

🎉 that's fantastic

//XCUIElementTypeTable/XCUIElementTypeCell/XCUIElementTypeStaticText[@name="XXX"]/parent::XCUIElementTypeCell/XCUIElementTypeStaticText
can ioschain implment like the above xpath? if can ,please give a exzample, thank you very much!