macron and breve combination

Dear All,

I have seen in printed books a combination of a macron ( ¯ ) with a breve
( ˘ ) above with or without an underlying vowel especially when dealing
with prosody. It shows that the vowel can be either long or short in
scansion.  I have checked a few Unicode blocks and have not yet seen this
combinination anywhere in use online, not even in the aritcles on prosody in
Wikipedia or Encyclopedia Britannica.

Does anyone have any idea how the combination can be rendered with a
keyboard if that is possible?

It's all part of an ongoing project to create a customized keyboard layout
with many capabilities.

Best wishes,

Jim