What semantic notions underlie 頁 ('page') with '預' ('beforehand')? I'm especially baffled because 'page' is physical, but 'beforehand' isn't physical. I screenshot Yellowbridge 



and quote 預 - Wiktionary.


  Phono-semantic compound (形聲, OC *las): phonetic 予 (OC *la, *laʔ) + semantic 頁.
  
  Definitions
  
  
  † beforehand
  † to take part in
  (Xiamen, Zhangzhou Min Nan) to participate in an activity
  (Xiamen, Zhangzhou, Taiwanese Hokkien) to play (chess, cards, mahjong, hide-and-seek, etc.)
  (Xiamen, Zhangzhou Min Nan, of an activity) to start
  (Cantonese, Teochew) to foresee; to expect; to anticipate
  
  
  
  我預咗佢會遲到㗎啦。 [Cantonese, trad.]
  我预咗佢会迟到㗎啦。 [Cantonese, simp.]
  
  
  Ngo5 jyu6 zo2 keoi5 wui5 ci4 dou3 gaa3 laa1. [Jyutping]
  
  I knew he was going to be late.
  (Cantonese, Teochew) to prepare; to plan for; to estimate
  
  今晚有朋友上嚟食飯，你預多啲飯餸喇喎。 [Cantonese, trad.]
  今晚有朋友上嚟食饭，你预多啲饭喇㖞。 [Cantonese, simp.]
  
  
  Gam1 maan5-1 jau5 pang4 jau5 soeng6 lai4 sik6 faan6, nei5 jyu6 do1 di1 faan6 sung3 laa3 wo3. [Jyutping]
  
  A friend is coming over for dinner tonight, so prepare more food.
  (Cantonese) to reserve a place; to count someone in
「預」 (Zhengzhang OC: /*las/, ahead/beforehand) is comprised of semantic 「頁」 (head) and phonetic 「予」 (/*laʔ/).

The components of a character contribute hints to the character based on what the components meant and/or sounded like at the time of the character's first appearance. 「頁」 (/*leb/) did not originally mean page; that meaning is a phonetic loan from 「葉」 (/*leb/, leaf &gt; flat sheet &gt; page).
「頁」 (head) was originally a picture of a kneeling person 「卩」 drawn with an emphasised head 「」 (now written 「首」). The legs of the kneeling person 「卩」 was later replaced with the legs of  「人」.

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Forms 1, 2, 4, 5 refer to 「頁」. Form 3 refers to 「項」.

When it is found in other characters, 「頁」 holds the meaning head (anatomy from the shoulders upwards) as a semantic hint. For example,

頭 head (+ phonetic 豆)

頸 neck (+ phonetic 巠)

領 neck &gt; collar (+ phonetic 令)

題 head &gt; main topic (+ phonetic 是)

額 forehead (+ phonetic 客)

頂 summit (+ phonetic 丁)