sleq(t, ws.BytesWritten(), wpex)
	rf(t, ws, []byte{})

	// seeks and reads.
	sk(t, ws, 1, io.SeekStart)
	rf(t, ws, []byte{2, 7})
	sk(t, ws, -2, io.SeekCurrent)
	rf(t, ws, []byte{2, 7})
	sk(t, ws, -4, io.SeekEnd)
	rf(t, ws, []byte{2, 7})
	off := sk(t, ws, 0, io.SeekEnd)
	sk(t, ws, off, io.SeekStart)

	// seek back and overwrite
	sk(t, ws, 1, io.SeekStart)
	wf(t, ws, []byte{9, 11})
	wpex = []byte{1, 9, 11, 8, 9}

since those use the underlying algorithm. This list is sent to the client if
it supports the server-sig-algs extension. Order is irrelevant.

Valid values
```
ssh-ed25519
sk******@****.***
sk******@****.***
ecdsa-sha2-nistp256
ecdsa-sha2-nistp384
ecdsa-sha2-nistp521
rsa-sha2-256
rsa-sha2-512
ssh-rsa
ssh-dss
```

//    Rule: Never break between consecutive runes of this category.
//
// 2) Mid:
//    MidLetter, MidNumLet, Single_Quote.
//    (Cf. case-ignorable: MidLetter, MidNumLet, Single_Quote or cat is Mn,
//    Me, Cf, Lm or Sk).
//    Rule: Don't break between Letter and Mid, but break between two Mids.
//
// 3) Break:
//    Any other category: NewLine, MidNum, CR, LF, Double_Quote, Katakana, and
//    Other.

qu: Runa Simi
rm: rumantsch grischun
rn: Ikirundi
ro: Română
ru: русский язык
rw: Ikinyarwanda
sa: संस्कृतम्
sc: sardu
sd: सिन्धी
se: Davvisámegiella
sg: yângâ tî sängö
si: සිංහල
sk: slovenčina
sl: slovenščina
sn: chiShona
so: Soomaaliga
sq: shqip
sr: српски језик
ss: SiSwati
st: Sesotho
su: Basa Sunda
sv: svenska
sw: Kiswahili
ta: தமிழ்
te: తెలుగు
tg: тоҷикӣ

000002e0  69 4b a8 51 ee de b3 b0  f7 1a 57 a3 28 72 d2 13  |iK.Q......W.(r..|
000002f0  a6 d3 17 0b c4 45 34 7f  10 3b 81 cb 0c 8d 51 b6  |.....E4..;....Q.|
00000300  0b 86 21 d0 ee 1d 7e 73  6b ea 77 8c 66 dc 65 16  |..!...~sk.w.f.e.|
00000310  03 03 00 04 0e 00 00 00                           |........|
>>> Flow 3 (client to server)
00000000  16 03 03 00 25 10 00 00  21 20 ed 3e ba a7 43 53  |....%...! .>..CS|

00000110  a9 54 af 0b 55 e2 d3 35  73 56 9b 9a 19 fd 93 9a  |.T..U..5sV......|
00000120  21 c3 5f f8 cf fe e0 a1  63 62 b8 58 bf 35 29 1d  |!._.....cb.X.5).|
00000130  69 58 f6 d3 e8 60 66 1b  db 53 4b 26 0b 78 d9 5e  |iX...`f..SK&.x.^|
00000140  73 d5 34 5a 11 57 98 8d  0c 9f 85 28 80 a4 ee 47  |s.4Z.W.....(...G|
00000150  f8 23 ca 31 7a 24 d5 dd  9b 49 7b 62 ab e5 69 fa  |.#.1z$...I{b..i.|