Excellent guidance notes on validation using the official CSL schema are provided in the Citation Styles page on zotero.org. Validation with the legal and multilingual schema version is similar, but uses an alternative URI for the schema address:
https://raw.github.com/fbennett/schema/v1.1mlz1/csl.rnc
For convenience, the Zotero instructions for online validation, but using this alternative schema address, are reproduced here:
- Select the style you want to validate. When using the “Address” option, provide the URL to the style. With “File Upload”, select the style file on your computer. With “Text Field”, paste the style code into the text box.
- Enter the URL to the CSL schema file in the “Schemas” text field. For CSL 1.0 with legal and multilingual extensions (MLZ), this is “https://github.com/fbennett/schema/master/csl.rnc”.
- Check the “Be lax about HTTP Content-Type” check-box and select the “XML; don’t load external entities” option in the “Parser” drop-down menu.
- Click the “Validate” button. If the style is correct, you will get the message “The document validates according to the specified schema(s) and to additional constraints checked by the validator.”. Only errors are important, warnings can be ignored.
(Thanks are due to Rintze Zelle, who prepared the original version of these instructions.)