Add note that the mps does not throw or catch exceptions, as suggested by rb <https://info.ravenbrook.com/mail/2014/10/09/15-07-32/0/>. gloss "freestanding" and "hosted" to help explain why.

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mps/manual/source/glossary/f.rst

@@ -414,10 +414,34 @@ Memory Management Glossary: F
 
         .. seealso:: :term:`free block`, :term:`free block chain`.
 
+
+    freestanding
+
+        In the :term:`C` programming language as defined by
+        :term:`C90`, a freestanding implementation "accepts any
+        strictly conforming program in which the use of the features
+        specified in the library section is confined to the contents
+        of the standard headers ``<float.h>``, ``<limits.h>``,
+        ``<stdarg.h>``, and ``<stddef.h>``." The :term:`C99` standard
+        adds ``<iso646.h>``, ``<stdbool.h>``, and ``<stdint.h>`` to
+        this list.
+
+        In particular, a freestanding implementation need not provide
+        the other features of the standard C library, including I/O,
+        time, and string operations.
+
+        .. opposite:: :term:`hosted`.
+
+        .. mps:specific::
+
+            The MPS is designed to be portable to a freestanding
+            implementation, by restricting the use of other features
+            either to :term:`platform`\-specific modules or to the
+            replaceable :term:`plinth` modules.
+
+        .. bibref:: :ref:`ISO/IEC 9899:1990 <C1990>`, :ref:`ISO/IEC 9899:1999 <C1999>`.
+
     free store
-
-        .. see:: :term:`heap`.
-
     freestore
 
         .. see:: :term:`heap`.

mps/manual/source/glossary/h.rst

@@ -98,6 +98,16 @@ Memory Management Glossary: H
 
         .. opposite:: :term:`miss rate`.
 
+    hosted
+
+        In the :term:`C` programming language, a hosted implementation
+        is one that provides all the features of the standard C
+        library.
+
+        .. opposite:: :term:`freestanding`.
+
+        .. bibref:: :ref:`ISO/IEC 9899:1990 <C1990>`, :ref:`ISO/IEC 9899:1999 <C1999>`.
+
     hot
 
         .. mps:specific::

mps/manual/source/topic/error.rst

@@ -8,12 +8,18 @@ Error handing
 =============
 
 Operations in the Memory Pool System that might fail return a
-:term:`result code` of type :c:type:`mps_res_t`, rather than a
-"special value" of the return type.
+:term:`result code` of type :c:type:`mps_res_t`. Success is always
+indicated by the result code :c:macro:`MPS_RES_OK`, which is defined
+to be zero. Other result codes indicate failure, and are non-zero. The
+MPS never uses a "special value" of some other type to indicate
+failure (such as returning ``NULL`` for a pointer result, or −1 for a
+size result).
 
-Success is always indicated by the result code :c:macro:`MPS_RES_OK`,
-which is defined to be zero. Other result codes indicate failure, and
-are non-zero.
+.. note::
+
+    The MPS does not throw or catch exceptions. (This is necessary
+    for the MPS to be portable to systems that have only a
+    :term:`freestanding` implementation of the C language.)
 
 The modular nature of the MPS means that it is not usually possible
 for a function description to list the possible error codes that it

mps/manual/source/topic/plinth.rst

@@ -22,8 +22,8 @@ The :dfn:`plinth` is a program module that provides the MPS with the
 support it needs from the execution environment. The MPS uses the plinth instead of (say) the Standard C Library because:
 
 #. The MPS is designed to be portable to systems that have only a
-   *conforming freestanding implementation* of the C language: that
-   is, systems which potentially lack some of the facilities of the
+   :term:`freestanding` implementation of the C language: that is,
+   systems which potentially lack some of the facilities of the
    Standard C Library, such as standard I/O. The plinth provides a way
    to map MPS requirements to the facilities provided on the platform,
    whatever they are.
@@ -39,17 +39,18 @@ facilities is included with the MPS, and this is good enough for most
 applications.
 
 There are many reasons why you might want to write your own plinth.
-You may be targeting a *freestanding environment* such as an embedded
-system. You might need to write the telemetry stream to a system
-logging facility, or transmit it over a serial port or network
-connection. Or you might need to direct debugging output to a
-convenient window in the user interface.
+You may be targeting an embedded system with only a
+:term:`freestanding` implementation of the C language. You might need
+to write the telemetry stream to a system logging facility, or
+transmit it over a serial port or network connection. Or you might
+need to direct debugging output to a convenient window in the user
+interface.
 
 The plinth is divided into two parts:
 
 #. The :ref:`topic-plinth-io` provides general-purpose I/O
-   functionality. It is used by the :term:`telemetry` system to output
-   a stream of events to assist with debugging and profiling.
+   functionality. It is used to output a :term:`telemetry stream` of
+   events to assist with debugging and profiling.
 
 #. The :ref:`topic-plinth-lib` provides miscellaneous functionality
    that would be available via the Standard C Library on a hosted
@@ -254,7 +255,7 @@ Library module
 
         In the ANSI Library module, ``mpsliban.c``, this reports the
         failure by calling ``fprintf(stderr, "...%s...", message)``,
-        flushes the :term:`telemetry` stream by calling
+        flushes the :term:`telemetry stream` by calling
         :c:func:`mps_telemetry_flush`, and, in the :term:`cool`
         :term:`variety`, terminates the program by calling
         :c:func:`abort`. You can change this behaviour with