按键帽序列

由数字或符号后接VS-16（U+FE0F）和组合包围键帽字符（U+20E3）构成的表情符号序列。

Keycap emoji represent keys on a telephone or keyboard. They are formed from three characters: a base character (0-9, *, or #), VS-16 to request emoji presentation, and U+20E3 (combining enclosing keycap) to add the visual key border.

For example, 2️⃣ is: `2` (U+0032) + `VS-16` (U+FE0F) + `⃣` (U+20E3). There are 12 keycap sequences in total: digits 0-9, asterisk (*), and hash (#).

These are among the oldest emoji sequences and demonstrate how Unicode combines existing characters with modifiers rather than assigning entirely new code points.