Horizontal Reflection Character

It means “mirror the next character component from left to right.”

An ideographic description sequence (IDS) is text notation for a character’s structure. ⿾ is an ideographic description character (IDC) that takes one following component: ⿾正 describes the left-to-right reflected form 𣥄. The sequence describes structure; it does not give 正 a new everyday meaning.

This notation lets researchers and cataloguers describe difficult forms and ideographs that lack their own encoded character.

how old is ⿾?

⿾ itself entered Unicode in 2023; the description notation is older.

A 1996 standards discussion treated ideographic description signs as operators with operands. A 1997 proposal used them to represent ideographs that did not yet have their own encoded characters.

A 2018 proposal included ⿾ among four new ideographic description characters. In 2022, a proposal described reflection and rotation as the first operators to take one following component and showed ⿾⿾正 as a case with no net effect. The 2023 encoding date is not the age of ideographic writing.

can ⿾ build a character?

No; it describes a shape but does not compose one.

An IDS is a text description, not an instruction that Unicode requires software to turn into a single glyph. Fonts or apps may show ⿾ and its operand as separate characters; that is consistent with the format.

Use ⿾ to record a component transformation. If you need the finished ideograph in running text, use that encoded character itself.