章 is used in: 文章 (article/essay), 章节 (chapter), 盖章 (stamp/seal), 规章 (regulation), 徽章 (badge). 盖章 (affixing a seal) is extremely important in Chinese bureaucracy and business.
Top 音 — sound/note. Original sense was a complete musical movement, a marked-off unit of sound, which extended to 'chapter, section, paragraph' and to 'seal, badge, regulation'. Indexed under Kangxi #117 立 (lì) by tradition; the radical sits buried in the upper 音 rather than as a visibly separate piece.
Bottom 十 — ten, here standing for completion or wholeness (as in 十全十美 'perfect in every way'). Together with 音 above: a complete, finished movement of music. From this came the abstract sense 'a complete chapter or section,' and by extension 'rule, regulation, stamp of authority.'
Filed under radical 立 (lì, #117) by convention. 立 is not a separate component in 章, so no strokes are highlighted.
