In Annex M of this draft, I found:

added memalignment function to query the alignment of a pointer;

and then its documentation:

7.24.9 Alignment of memory
7.24.9.1 The memalignment function

Synopsis

#include <stdlib.h> size_t memalignment(const void *p);

Description

The memalignment function accepts a pointer to any object and returns the maximum
alignment satisfied by its address value. The alignment may be an
extended alignment and may also be beyond the range supported by the
implementation for explicit use by alignas. 359) If so, it will
satisfy all alignments usable by the implementation. The value
returned can be compared to the result of alignof, and if it is
greater or equal, the alignment requirement for the type operand is
satisfied.

Returns

The alignment of the pointer p, which is a power of two. If p is a null pointer, an alignment of zero is returned.

NOTE

An alignment of zero indicates that the tested pointer cannot be
used to access an object of any type.

Question: What do “maximum alignment” and “extended alignment” mean in layman’s terms, and can’t the alignment of a pointer be found with the alignof operator?