Which keyword is defined as flexible for input contexts?

The In keyword is used to define an explicit output context for a measure calculation, restricting results to a named set of dimensions, and is not classified as flexible for input contexts.

All is a keyword used to remove all dimensions from the calculation context, computing a measure at the most aggregated level, and is not specifically characterized as flexible for input contexts.

ForAll is used to exclude specific dimensions from the calculation context, and while it modifies context, it is not the keyword defined as flexible for input contexts.

ForEach is designated as a flexible input context keyword because it allows report writers to explicitly add dimensions to the calculation context of a measure, overriding the default context determined by the block structure. This flexibility makes it useful for computing measures at a more granular level than what the current block provides.