We don't parse the content of the cover letter only. Any CV/Resume contains a cover letter along with the candidate profile summary, RChilli parser will parse information accordingly. But if the candidate has not mentioned the profile summary with cover letter, then again it won't parse.
We distinguish the parsed information which we are receiving from both the candidate's resume and cover letters, along with parsed data. We are able to recognize and send the type of document, whether the Document is Resume or Cover Letter.
We are providing the cover letter content in the "Coverletter:" field in JSON Output, where you can see the extracted data for cover letter.