def heading_mark(title, char):
    """
    Given an input title and character, creates the reStructuredText underline
    according to the length of the title.

    **Parameters**
        **title** (str)
            The title that is being underlined, length assumed to be >= 1.

        **char** (str)
            The single character being used for this heading, e.g.
            :data:`~exhale.configs.SECTION_HEADING_CHAR`.

    **Return**
        **str**
            Returns ``len(title) * char``.
    """
    return len(title) * char
