To guarantee that an extension field is processed with its associated extension, the extension query part must escape any special characters like '*' or '['. If the extension query contains any whitespace characters, the extension query part must be enclosed in quotes. Example ('_' used as separation character):
title_customExt:"Apache Lucene\?" OR content_customExt:prefix\*Search on the default field:
_customExt:"Apache Lucene\?" OR _customExt:prefix\*
The ExtendableQueryParser itself does not implement the logic how field and extension key are separated or ordered. All logic regarding the extension key and field symbol parsing is located in Extensions. Customized extension schemes should be implemented by sub-classing Extensions.
For details about the default encoding scheme see Extensions.
Extensions ParserExtension ExtensionQuery