gene_constraint parameter documentation needs to be clarified

[enaix]

Hello, from the documentation it's not clear which values are contained in the solution variable:

When assigned a list, the allowed values for each element are:

1. None: No constraint for the gene.
2. callable: A callable/function that accepts 2 parameters:
   1. The solution where the gene exists.
   2. A list or NumPy array of candidate values for the gene.

Either all of the solution values may either be the unchanged solution (before the mutation), or solution values are updated incrementally at each step. In mutation_by_space and mutation_probs_by_space it seems to be updated incrementally (in i-th gene constraint solution[:i] are updated and solutions[i:] are from the original population AFAIK)

It would be nice if this could be described in slightly more detail
Thanks!