What is the usage of as to what?

The phrase "as to what" is typically used to introduce a question or inquiry about a specific detail or aspect of something. It's often used to ask for clarification or further information.

Here are some examples:

* "I'm not sure as to what time the meeting is." This means the speaker is unsure about the meeting's time and wants to know it.

* "Could you tell me as to what your plans are for the weekend?" This is asking for details about the listener's weekend plans.

* "The report is unclear as to what the main findings are." This means the report lacks a clear statement of its key findings.

Note:

* "As to what" is generally considered more formal than simply saying "what."

* It can sometimes sound a bit stilted or archaic, so using it cautiously is recommended.

In most cases, you can replace "as to what" with just "what" without changing the meaning significantly.