+ * Opens a stream which reads from or writes to a space in memory. @buf points
+ * to the buffer where output will be read from or written to. @buflen is the
+ * length of the buffer.
+ *
+ * When outputting, if more than @buflen characters are written to the stream,
+ * all of them beyond the buffer length will be thrown away, so as not to
+ * overwrite the buffer. (The character count of the stream will still be
+ * maintained correctly. That is, it will count the number of characters written
+ * into the stream, not the number that fit into the buffer.)
+ *
+ * If @buf is %NULL, or for that matter if @buflen is zero, then <emphasis>
+ * everything</emphasis> written to the stream is thrown away. This may be
+ * useful if you are interested in the character count.
+ *
+ * When inputting, if more than @buflen characters are read from the stream, the
+ * stream will start returning -1 (signalling end-of-file.) If @buf is %NULL,
+ * the stream will always return end-of-file.
+ *
+ * The data is written to the buffer exactly as it was passed to the printing
+ * functions (glk_put_char(), etc.); input functions will read the data exactly
+ * as it exists in memory. No platform-dependent cookery will be done on it.
+ * (You can write a disk file in text mode, but a memory stream is effectively
+ * always in binary mode.)
+ *
+ * Unicode values (characters greater than 255) cannot be written to the buffer.
+ * If you try, they will be stored as 0x3F ("?") characters.
+ *
+ * Whether reading or writing, the contents of the buffer are undefined until
+ * the stream is closed. The library may store the data there as it is written,
+ * or deposit it all in a lump when the stream is closed. It is illegal to
+ * change the contents of the buffer while the stream is open.