The following characters have special behavior in Minecraft, and care should be taken when retexturing them in a custom font:
Unusable
\u0000
: NULL �- This character cannot be included in a bitmap font, since it's used as a placeholder to skip certain cells of the texture grid.
\u000a
: LINE FEED ⏎- This character can be retextured and appear in text that does not support multiple lines. In chat, it will be invisible and cause a line break.
\u00a7
: SECTION SIGN §- This character is never displayed. It also prevents the next character from displaying, and activates legacy formatting.