channeling:<spell name>

Normally, if you are channeling a spell and begin casting another spell, it will cancel the channel. This option allows you to keep that from happening, and also has a few other uses. For instance, maybe you do want to cancel one particular spell but not another. [channeling] alone matches any spell and you can also list an arbitrary number of spell names to check.
Note: channeling is NOT the same as casting. The [channeling] conditional only applies to spells like Arcane Missiles, Drain Life, Mind Flay, etc. where after the initial cast, the spell makes its effect over time.
from WoWwiki