Constant RE_DOI_TEXT 

pub const RE_DOI_TEXT: &str = r#"^(?<schema_uri>https[:]\/\/doi\.org\/)?(?<directory_indicator>10).(?<registrant_code>\d{4,9})\/(?<suffix>[-._;()/:a-zA-Z0-9]+)$"#;

Pattern text for DOI regular expression defined by RE_DOI