The description of define-record-type does not explicitly make clear the
mutability of the last two <field spec>

              -> (<field name> <accessor name>)
              -> (<field name> <accessor name> <mutator name>)

The description defers to SRFI-9 for these but SRFI-9 does not mention
their mutability.  Like the first two <field spec> introduced by this
SRFI, the mutability should be clearly stated, to make clear that
mutator procedures cannot manually (via rtd-mutator) be got for
immutable fields.

--
: Derick
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