Block functions are a subset of Twaddle functions. Rather than taking effect wherever they are encountered in the Twaddle sentence, they set parameters for the next block. This will typically be placed immediately after the function definition. This is not required to be the case, and the effect will still apply to the next block even when they are separated.
For example:
[hide]some {secret }stuff
prints:
some stuff
This is because the hide function hides the next block, regardless of
any gaps between the function and the block.
The effect of the block function will apply to the next block to open, when reading the sentence left-to-right. This occurs even if the block function is contained within a block itself, allowing for block functions to be set variably based on branching paths.