I used Parse Rule XML from Create a new LanguageTool rule on this syntactically incorrect rule:
<rule id="RULE_EDITOR_TEST" name="Rule Editor Test">
<pattern>
<token regexp="yes">bucket|flower pot|spade|</token>
</pattern>
<message>Did you mean <suggestion>equipment</suggestion>?</message>
<example correction="Michael">Put the <marker>bucket</marker> in the shed.</example>
<example>This <marker>equipment</marker> is dirty.</example>
</rule>
The Rule Editor did not give a warning about the incorrect syntax.