I like LEGO and JavaScript.

block.js

( function ( self ) {
	var library = {};

	var GlobalDomain = {
		instances: {},
		getInstance: function ( name ) {
			var instance = this.instances[ name ] || ( typeof library[ name ] == 'function' ? library[ name ]() : library[ name ] );
			this.instances[ name ] = instance;
			return instance;
		}
	}

	function register ( name, value ) {
		if ( library[ name ] ) {
			throw Error( 'Block '+ name +' already registered.' );
		}
		library[ name ] = value;
	}

	function use ( name, domain ) {
		if ( !library[ name ] ) {
			throw Error( 'Block '+ name +' not registered.' );
		}

		domain = domain || GlobalDomain;

		return domain.getInstance( name );
	}

	self.use = use;
	self.register = register;
	self.register.library = library;
} )( self );

core-pieces.js

register( 'core/pieces', function ( ) {
	var pieces = {};
	
	function PiecesDomainForElement ( element ) {
		return {
			getInstance: function ( name ) {
				var instance = element[ 'block-instance-of-'+ name ] || ( typeof register.library[ name ] == 'function' ? register.library[ name ]( element ) : register.library[ name ] );
				element[ 'block-instance-of-'+ name ] = instance;
				return instance;
			}
		};
	}
	
	pieces.init = function ( ) {
		pieces.load( document );
	}
	
	pieces.load = function ( element ) {
		if ( element.dataset && ( element.dataset.piece || element.dataset.pieces ) ) {
			pieces.loadForElement( element );
		}
		Array.prototype.forEach.call( element.querySelectorAll( '[data-piece], [data-pieces]' ), pieces.loadForElement );
	}
	
	pieces.loadForElement = function ( element ) {
		var blocks = [];
		element.dataset.piece && blocks.push( element.dataset.piece );
		element.dataset.pieces && blocks.concat( element.dataset.pieces.split( /\s+/g ) );
		
		blocks.forEach( function ( block ) {
			use( block, PiecesDomainForElement( element ) );
		} );
	}
	
	return pieces;
} );