explain xkcd:User: Aprilfoolsupdate!

Wow what? I can create my user page now! Yay!
About me: basic knowledge of html, nothing else
My signature: ^April_fools^update!(talk)
I like my signature, don’t touch it.
Leaderboard for top 50:

Aprilfoolsupdate!
Aprilfoolsupdate!
Born date	Not telling
Planet	Earth [citation needed]
Language	English
Stellar system	The solar system

Last 7 days (Top 50)

Rank Score Pages Changes Username 1 4,981 4,966 5,024 DollarStoreBa'al 2 1,848 1,831 1,907 Victoria 3 23 18 24 TheusafBOT 4 11 5 13 Trimutius 5 10 7 10 FaviFake 6 9 6 8 Utdtutyabthsc 7 8 5 8 Lp0 on fire 8 7 5 6 R128 9 7 2 8 boB 10 6 3 5 BunsenH 11 5 3 4 Mathmaster 12 4 1 4 NotBob 13 4 2 3 Barry Margolin 14 4 2 3 Fephisto 15 3 1 2 Kirinhatchi 16 3 1 2 Questioner 17 3 3 3 KelOfTheStars! 18 3 1 2 Beechmere 19 3 1 2 TheSeventhElectron 20 3 3 3 Batbrain55 21 3 1 2 Kynde 22 3 3 3 Starnote 23 3 1 2 Paul 24 3 1 2 Stephan Leeds 25 2 2 2 Theusaf 26 2 2 2 RadiantRainwing 27 2 2 2 AgentMuffin 28 2 2 2 August Fuller 29 1 1 1 1234231587678 30 1 1 1 Magtei 31 1 1 1 StepSquadStepped 32 1 1 1 Ardub 33 1 1 1 183231bcb 34 1 1 1 Michael Valler 35 1 1 1 Frigidus08 36 1 1 1 DKMell 37 1 1 1 Neike Taika-Tessaro 38 1 1 1 Dbwiddis 39 1 1 1 Geometrist 40 1 1 1 Daniel Griscom 41 1 1 1 Coconut Galaxy 42 1 1 1 GreatWyrmGold 43 1 1 1 X 44 1 1 1 CalibansCreations 45 1 1 1 Bdentremont 46 1 1 1 LazyTiger0203 47 1 1 1 David Garfield 48 1 1 1 Hellousern 49 1 1 1 Nvidietha