UTF-8 uses variable-width encoding. Codepoints in U+0000–U+007F (ASCII) take 1 byte; U+0080–U+07FF take 2 bytes; U+0800–U+FFFF take 3 bytes (this includes most CJK in the BMP); U+10000–U+10FFFF take 4 bytes (most emoji, ancient scripts, CJK Extension B+). A "simple" emoji like 😀 (U+1F600) is in Plane 1 so it's 4 UTF-8 bytes, while the heart ❤ (U+2764) is in the BMP Dingbats block and only takes 3 bytes.

Country flags don't have their own codepoints. Each flag is a sequence of two regional indicator symbols in the range U+1F1E6–U+1F1FF (which correspond to the letters A–Z). 🇺🇸 is U+1F1FA (regional indicator U) + U+1F1F8 (regional indicator S). The font sees the pair and renders the US flag; if the font doesn't have flag support, you see two letter boxes. Of the 676 possible AA–ZZ pairs, only the ~270 matching ISO 3166-1 alpha-2 country codes render as flags. In UTF-8 each flag takes 8 bytes (two 4-byte astrals); in UTF-16 it's 8 bytes (two surrogate pairs).

Combining characters modify the base character that precedes them — primarily accents and diacritics. The combining range U+0300–U+036F includes U+0301 combining acute (̀), U+0308 combining diaeresis (̈), U+0303 combining tilde, and others. So é can be stored as a single precomposed codepoint U+00E9 (NFC form) or as e + U+0301 (NFD form) — both display identically but compare unequal in byte-wise string comparison. Use Unicode normalization (String.prototype.normalize('NFC') in JS, unicodedata.normalize in Python) before comparing or storing user input. "Zalgo" text is just dozens of combining