creates a new base type
   (scalar type).  To create a new base type, you must be a superuser.
   (This restriction is made because an erroneous type definition could
   confuse or even crash the server.)
  </para>

  <para>
   The parameters can appear in any order, not only that
   illustrated above, and most are optional.  You must register
   two or more functions (using <command>CREATE FUNCTION</command>) before
   defining the type.  The support functions
   <replaceable class="parameter">input_function</replaceable> and
   <replaceable class="parameter">output_function</replaceable>
   are required, while the functions
   <replaceable class="parameter">receive_function</replaceable>,
   <replaceable class="parameter">send_function</replaceable>,
   <replaceable class="parameter">type_modifier_input_function</replaceable>,
   <replaceable class="parameter">type_modifier_output_function</replaceable>,
   <replaceable class="parameter">analyze_function</replaceable>, and
   <replaceable class="parameter">subscript_function</replaceable>
   are optional.  Generally these functions have to be coded in C
   or another low-level language.
  </para>

  <para>
   The <replaceable class="parameter">input_function</replaceable>
   converts the type's external textual representation to the internal
   representation used by the operators and functions defined for the type.
   <replaceable class="parameter">output_function</replaceable>
   performs the reverse transformation.  The input function can be
   declared as taking one argument of type <type>cstring</type>,
   or as taking three arguments of types
   <type>cstring</type>, <type>oid</type>, <type>integer</type>.
   The first argument is the input text as a C string, the second
   argument is the type's own OID (except for array types, which instead
   receive their element type's OID),
   and the third is the <literal>typmod</literal> of the destination column, if known
   (-1 will be passed if not).
   The input function must return a value of the data type itself.
   Usually, an input function should be declared STRICT; if it is not,
   it will be called with a NULL first parameter when reading a NULL
   input value.  The function must still return NULL in this case, unless
   it raises an error.
   (This case is mainly meant to support domain input functions, which
   might need to reject NULL inputs.)
   The output function must be
   declared as taking one argument of the new data type.
   The output function must return type <type>cstring</type>.
   Output functions are not invoked for NULL values.
  </para>

  <para>
   The optional <replaceable class="parameter">receive_function</replaceable>
   converts the type's external binary representation to the internal
   representation.  If this function is not supplied, the type cannot
   participate in binary input.  The binary representation should be
   chosen to be cheap to convert to internal form, while being reasonably
   portable.  (For example, the standard integer data types use network
   byte order as the external binary representation, while the internal
   representation is in the machine's native byte order.)  The receive
   function should perform adequate checking to ensure that the value is
   valid.
   The receive function can be declared as taking one argument of type
   <type>internal</type>, or as taking three arguments of types
   <type>internal</type>, <type>oid</type>, <type>integer</type>.
   The first argument is a pointer to a <type>StringInfo</type> buffer
   holding the received byte string; the optional arguments are the
   same as for the text input function.
   The receive function must return a value of the data type itself.
   Usually, a receive function should be declared STRICT; if it is not,
   it will be called with a NULL first parameter when reading a NULL
   input value.  The function must still return NULL in this case, unless
   it raises an error.
   (This case is mainly meant to