FormHelperText
Helper or error text for a field, built on Typography and rendered as a <p>. Reads its id and error state from FormControl context and registers its presence so the control points aria-describedby at it only while it is rendered.
Architecture: FormHelperText renders Typography as="p". id resolves to the explicit prop, else the FormControl helperId (${id}-helper). When error is set (or inherited from FormControl), it renders in color="error" and sets role="alert" so changes are announced. On mount it calls the FormControl's stable setHasHelperText(true) and clears it on unmount - that flag drives aria-describedby on the control, so a reference is only present when the text is.
Examples
Default
We'll never share it.
<FormHelperText>We'll never share it.</FormHelperText>
Error State
Enter a valid e-mail address.
<FormHelperText error>Enter a valid e-mail address.</FormHelperText>
From Context
Enter a valid e-mail address.
<FormControl id="email" error>
<FormHelperText>Enter a valid e-mail address.</FormHelperText>
</FormControl>