docs - identify enum type support for GUCs
<topic id="topic_vsn_22l_z4">
<title>Parameter Types and Values</title>
<body>
- <p>All parameter names are case-insensitive. Every parameter takes a value of one of four
- types: <codeph>Boolean</codeph>, <codeph>integer</codeph>, <codeph>floating point</codeph>,
- or <codeph>string</codeph>. Boolean values may be written as <codeph>ON</codeph>,
+ <p>All parameter names are case-insensitive. Every parameter takes a value of one of the
+ following types: <codeph>Boolean</codeph>, <codeph>integer</codeph>, <codeph>floating point</codeph>,
+ <codeph>enum</codeph>, or <codeph>string</codeph>.</p>
+ <p>Boolean values may be specified as <codeph>ON</codeph>,
<codeph>OFF</codeph>, <codeph>TRUE</codeph>, <codeph>FALSE</codeph>, <codeph>YES</codeph>,
<codeph>NO</codeph>, <codeph>1</codeph>, <codeph>0</codeph> (all case-insensitive).</p>
+ <p>Enum-type parameters are specified in the same manner as string parameters, but are
+ restricted to a limited set of values. Enum parameter values are case-insensitive.</p>
<p>Some settings specify a memory size or time value. Each of these has an implicit unit,
which is either kilobytes, blocks (typically eight kilobytes), milliseconds, seconds, or
minutes. Valid memory size units are <codeph>kB</codeph> (kilobytes), <codeph>MB</codeph>
