+ * Programming style:
+ *
+ * The following style provides sufficient error
+ * checking for this routine, with minimal clutter
+ * in the source code. It is recommended if you
+ * have many calls to this function:
+ *
+ * char * s = strdup(...); // don't check for error
+ * string_append(&s, ...); // don't check for error
+ * string_append(&s, ...); // don't check for error
+ * string_append(&s, ...); // don't check for error
+ * if (NULL == s) { ... handle error ... }
+ *
+ * OR, equivalently:
+ *
+ * char * s = strdup(...); // don't check for error
+ * string_append(&s, ...); // don't check for error
+ * string_append(&s, ...); // don't check for error
+ * if (string_append(&s, ...)) {... handle error ...}
+ *