On gaining moves out of your class.

I have the faint idea that somewhere i read that you could gain moves outside of your class. I.E.: a PC has been constantly researching arcane lore and grimoires and has made some quest in favor of a School of Magi or perhaps has been graced with the blessings of a god of magic and through it's efforts gains access to Cast a Spell and some rotes (without leveling up and learning it).
I know i can house rule it, but i'm just interested to know if anybody read something like it in earlier threads or blogs or something on those lines and could direct me to the relevant posts.

Side note: what do you think of the idea?

Straight from the rules text (Chapter: Playing the Game):

Character Change

Dungeon World is ever-changing. The characters change, too. As their adventures progress, player characters gain experience or XP, which lets them level up. This prepares them for greater danger, bigger adventures, and mightier deeds.

Advancement, like everything else in Dungeon World, is both prescriptive and descriptive. Prescriptive means that when a player changes their character sheet the character changes in the ficiton. Descriptive means that when the character changes in the fiction the player should change the character sheet to match.

This isn't a benefit or detriment to the players or the GM; it's not an excuse to gain more powers or take them away. It's just a reflection of life in Dungeon World.

Avon, despite being a Wizard, has risen to the notice of Lenoral, the deity of arcane knowledge. After being blessed by an avatar of Lenoral and saying his vows in the church, Avon is under the deity's watch. He can fulfill Petitions and gain boons like a Cleric.

Gregor offers his signature weapon, an axe whose green steel is tempered in orc blood, as a desperate bargain to save King Authen from eternal damnation. Without his axe he gets none of the benefits of his signature weapon. Should he recover it he'll have access to its benefits again.

Descriptive changes only happen when the character has clearly gained access to an ability. It’s not up to any one player to decide this—if you think a character qualifies for a new ability, discuss it as a group.

Thanks! I knew i read it somewhere and it was driving me crazy forgetting where the concept came from. I think it speaks in behalf of my memory...

Also, most of the classes have a multi-class move which lets them take a move from another class.

Indeed and i love that option, it leaves a world of choices for your character (mechanically speaking) that will drive who he is into new horizons :)