To give you an idea of what it means, this is what is on the Visitor/ Visitor in Transit (sponsor) form:
Monthly income/deposit (HK$)
Sponsor’s Statement and Declaration
I consent to the making of any enquiries necessary for the processing of this application.
I certify from my personal knowledge of the applicant, that I am able to support the applicant as a person whom I believe is suitable to be allowed into Hong Kong for the purpose stated.
I undertake to assume responsibility for the applicant’s repatriation to (insert place of domicile) if at the expiry of limit of stay granted by the Director of Immigration, the applicant fails to leave Hong Kong.