: new RegExp(source)
}

const isString = subject => typeof subject === 'string'

// > A blank line matches no files, so it can serve as a separator for readability.
const checkPattern = pattern => pattern
    && isString(pattern)
    && !REGEX_TEST_BLANK_LINE.test(pattern)
    && !REGEX_INVALID_TRAILING_BACKSLASH.test(pattern)

    // > A line starting with # serves as a comment.