502.40a.

Splice is a static ability that functions while a card is in your hand. "Splice onto [type or subtype] [cost]" means "You may reveal this card from your hand as you play a [type or subtype] spell. If you do, copy this card's text box onto that spell and pay [cost] as an additional cost to play that spell." Paying a card's splice cost follows the rules for paying additional costs in rules 409.1b and 409.1f-h.

Example: Since the card with splice remains in the player's hand, it can later be played normally or spliced onto another spell. It can even be discarded to pay a "discard a card" cost of the spell it's spliced onto.