Function ancestor_source_list_is_valid 

pub fn ancestor_source_list_is_valid(list: &SourceList) -> bool

Whether list only contains expressions valid in frame-ancestors’ restricted ancestor-source-list: scheme-source, host-source, and 'self' – unlike a regular source-list, no 'unsafe-inline' (or any other keyword), no nonce-source, no hash-source. Unrecognized entries (expression: None) also make the list invalid.