Fix the `head` elements of Xilem Web #768

Job	Run time
cargo check (msrv) (windows-latest)	3m 16s
cargo clippy (windows-latest)	4m 41s
cargo check (msrv) (wasm32)	27s
cargo check (msrv) (macos-latest)	1m 22s
cargo clippy (macos-latest)	1m 57s
cargo check (aarch64-android)	1m 40s
cargo clippy (ubuntu-latest)	2m 22s
cargo check (msrv) (ubuntu-latest)	1m 26s
cargo clippy (wasm32)	1m 9s
cargo doc	1m 27s
cargo fmt	32s
cargo test (windows-latest)	4m 39s
cargo test (macos-latest)	2m 7s
cargo test (wasm32)	47s
typos	3s
cargo test (ubuntu-latest)	3m 51s
	31m 46s

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