I'm very keen to know how could I enter a Data Validation expression using
tables.

I have two sheets with two tables. In a certain column of the first I need
to restrict the values one can enter to the values entered in a column in the
other table.

So for ColumnX in Table1, I'd like to set a custom data validation
expression like:
=Table2[ColumnY]
to tell only values in the ColumnY column are enabled to be entered in
ColumnX.

Is there a way to do this or isn't this stuff supported?