value for aria textbox role

Regarding the aria textbox role - is there an attribute which would reveal
the value of the textbox to assistive technology as required by SC 4.1.2?
That is to say, when an HTML input is used then the value of that input is
determinable by AT. However, if a custom control is made using
non-interactive elements, and using the aria textbox role, how would the
value be determined? The same question would apply for the combobox widget.
The value of the widget might very well be implicitly determined by the
value of the html input associated with that widget. But, is there an
aria-based attribute for this determination, especially in a case where an
html input is not used in the widget?

Thank you in advance for your feedback.