use `u5` and `u27` in public API #247

Job	Run time
clippy (ubuntu-latest)	57s
rustfmt	13s
clippy (macos-latest)	1m 5s
miri (ubuntu-latest)	2m 0s
miri (macos-latest)	2m 14s
cross (aarch64-unknown-linux-gnu)	52s
clippy (windows-latest)	1m 8s
cross (aarch64-linux-android)	51s
sanitizer (ubuntu-latest)	1m 35s
cross (aarch64-unknown-linux-musl)	48s
test (ubuntu-latest)	1m 19s
cross (i686-linux-android)	50s
valgrind	56s
test (macos-latest)	1m 37s
cross (x86_64-linux-android)	51s
cross (i686-pc-windows-gnu)	49s
test (windows-latest)	1m 29s
cross (x86_64-pc-windows-gnu)	45s
cross (i686-unknown-linux-gnu)	50s
cross (powerpc64-unknown-linux-gnu)	50s
cross (riscv64gc-unknown-linux-gnu)	46s
cross (wasm32-unknown-unknown)	35s
cross (wasm32-unknown-emscripten)	49s
cargo tarpaulin	0s
	24m 9s

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