Variation Selector-31

It selects a registered glyph variant after a CJK character.

Here, “glyph” means the drawn shape, not a new character or meaning. VS31 belongs to the supplementary ideographic-selector range. Its effect depends on the preceding base character and a registered entry in Unicode’s Ideographic Variation Database; it is not a universal “thirty-first style.”

VS31 has no historical sign tradition of its own. The problem it solves comes from regional, historical, scholarly, government, and publishing traditions that need different shapes for related Han characters. Unicode’s 2003 design discussions made it possible to carry those distinctions in plain text without encoding every glyph as a new character. The selector was encoded in Unicode 4.0 in 2003.

why is U+E010E invisible?

Because the selector has no visible shape of its own.

Fonts that support a registered pair can store its glyph mapping in OpenType Format 14 variation data. If the pair is valid but unsupported, normal rendering shows the base as if the selector were absent. A selector placed alone is a misplaced selector, not a standalone instruction; a diagnostic “show hidden” mode may expose it.

One registered example pairs U+9089 邉 with VS31 in the Adobe-Japan1 collection. That pair identifies a particular Japanese glyph record; VS31 does not carry the same choice into other ideographs. The useful unit is the whole sequence, not the invisible selector by itself.