Now that's just too strange. When I right-click a cell with an 'old'
validation rule I get a 'Validate data...' option in the context menu for
that cell. When I create an equivalent 'new' validation rule and
right-click on a cell protected by the rule, I don't get that option,
although the cell still has a note saying that its invalid. It's only the
'old' type of validation which prevents insertion of a table <entry/> into
the feed. At first I thought it might have been defining the validation on
the whole *column* instead of just a single cell. But no - at least with a
'new' validation, it doesn't matter if its on cell of row 1' or the whole
column.
