I have encountered SLDs which use an ElseFilter, see this link .

The is not yet supported. This is used akin to , etc.

I came across SLDs that use this function to style a layer when an attribute attains a value that occurs in some list. Example found:

<ogc:PropertyIsEqualTo>
	<ogc:Function name="in">
		<ogc:PropertyName>visualisatiecode</ogc:PropertyName>
		<ogc:Literal><![CDATA[11300]]></ogc:Literal>
		<ogc:Literal><![CDATA[11301]]></ogc:Literal>
		<ogc:Literal><![CDATA[11302]]></ogc:Literal>
	</ogc:Function>
	<ogc:Literal>true</ogc:Literal>
</ogc:PropertyIsEqualTo>

This function is not yet supported in the parser.

Nested logical operators are not yet supported in the parser. These should translate to a WHERE-clause which reads something like

SELECT *
FROM table
WHERE attribute1 = x AND (attribute2 = y OR attribute2 = z)

String values in SQL should escape single quotes to prevent SQL errors (or sql insertion)