Spontaneity in Zen

This [Zen Buddhism](http://www.bbc.co.uk/religion/religions/buddhism/subdivisions/zen_1.shtml) article starts with, > Zen often seems paradoxical - it requires an intense discipline which, when practised properly, results in total spontaneity and ultimate freedom. This natural spontaneity should not be confused with impulsiveness. What would they mean by "intense discipline" there, for example ... is it the routine in a monastery? More centrally, to this question, what is the role of "spontaneity"? Is it a goal? A means to the goal? A side-effect or symptom of having reached "the goal"? Is spontaneity *practised* somehow, or is that a paradox? Is there famous (written and translated) Zen doctrine on the subject ... an explanation by someone? Does it (or something like it) exist, as a value or as a goal or whatever it is, in other schools of Buddhism (e.g. Theravada, or ...)? Is it spontaneity but within some limits? For example, within the limits of "ethical rules" ... or within the limits of, I don't know, calligraphic and/or other arts, for example? Assuming it's a well-known concept, is "spontaneity" the right word, the right translation for it? What could be other translations? What's the original (pre-translated) word or words?