What semantic notions underlie 頁 ('page') with '預' ('beforehand')?
「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)