From D'Addario:

XL Nickel Wound electric guitar strings are the standard against which all other strings are measured. Our best-belling electric set, XL Nickel has been revered by players everywhere since 1974. Made with a high carbon steel core and nickel-plated steel wrap wire, XL Nickel strings have a bright, versatile tone, ideal for a wide variety of musical styles. This 10-46 Regular Light 12-String set is the most popular choice for 12-string electric guitars, providing the ideal balance of comfortable feel and bright, jangly tone.