For general linguistics, the Combining half marks are not recommended for usage. Instead, U+0360 COMBINING DOUBLE TILDE and U+0361 COMBINING DOUBLE INVERTED BREVE are the preferred characters to use.
Thus, to put the U+0361 COMBINING DOUBLE INVERTED BREVE over an “ia”, the preferred encoding would be to put the U+0361 between “ia” (i + U+0361 + a):
However, there are four diacritics that can produce a similar display. These are used within the Latin-script in the library world: U+FE20..U+FE23.
|U+FE20 COMBINING LIGATURE LEFT HALF|
|U+FE21 COMBINING LIGATURE RIGHT HALF|
|U+FE22 COMBINING DOUBLE TILDE LEFT HALF|
|U+FE23 COMBINING DOUBLE TILDE RIGHT HALF|
Transliterated Cyrillic records also make heavy use of the first two.
An example of how they can be used is below. Positioning of these may not be perfect.