Many people are opposed to single sentence spacing for various reasons. Some state that the habit of double spacing is too deeply ingrained to change. Others claim that additional space between sentences improves the aesthetics or readability of text. Proponents of double sentence spacing also state that some publishers may still require double-spaced manuscript submissions from authors. A key example noted is the screenwriting industry's monospaced standard for screenplay manuscripts, Courier, 12-point font, although some works on screenwriting indicate that Courier is merely preferred—proportional fonts may be used. Some reliable sources state simply that writers should follow their particular style guide, but proponents of double spacing caution that publishers' guidance takes precedence, including those that ask for double sentence spaced manuscripts.