Based on the Peter L. Jones syntax highlighting sfz language file for Notepad++.

• In Notepad++: menu Language > User Defined Language > Define your language...
• In the User Defined dialog click the Import... button
• Select the sfz-udl.xml file
• Close the dialog window

• If a header and an opcode have no whitespace in between, the syntax highlighting will not work (e.g. <region>sample=audio.wav)
• Opcodes with numbers in between like egN or lfoN are not specified, resulting to highlight anything with the eg or lfo prefix