Rephrase documentation

Author: sdesmalen-arm

clang/include/clang/Basic/AttrDocs.td

@@ -7639,16 +7639,22 @@ def ArmAgnosticDocs : Documentation {
   let Category = DocCatArmSmeAttributes;
   let Content = [{
 The ``__arm_agnostic`` keyword applies to prototyped function types and
-specifies that the function is agnostic about the given state S and
-returns with state S unchanged if state S exists.
+affects the function's calling convention for a given state S. This
+attribute allows the user to describe a function that preserves S, without
+requiring the function to share S with its callers and without the making
+the assumption that S exists.
 
-The attribute takes string arguments to instruct the compiler which state
-the function is agnostic about.  The supported states for S are:
+If a function has the ``__arm_agnostic(S)`` attribute and calls a function
+without this attribute, then the function's object code will contain code
+to preserve state S. Otherwise, the function's object code will be the same
+as if it did not have the attribute.
+
+The attribute takes string arguments to describe state S. The supported
+states are:
 
-* ``"sme_za_state"`` for any state enabled by PSTATE.ZA (including the
-  bit itself)
+* ``"sme_za_state"`` for state enabled by PSTATE.ZA, such as ZA and ZT0.
 
-The attributes ``__arm_agnostic("sme_za_state")`` cannot be used in conjunction
+The attribute ``__arm_agnostic("sme_za_state")`` cannot be used in conjunction
 with ``__arm_in(S)``, ``__arm_out(S)``, ``__arm_inout(S)`` or
 ``__arm_preserves(S)`` where state S describes state enabled by PSTATE.ZA,
 such as "za" or "zt0".