This is the current correct syntax for tables:

This

||head1||head2
|field11|field12
|field21|field22

This syntax is more intuitive (table-like):

This

||head1||head2||
|field11|field12|
|field21|field22|

The additional '|' at the right produces an additional column. Someone might consider this a bug.

I would also like to see a way to span a cell so if I was to do

This

||head1||head2||
|field11|field12|
|field21

it would produces a table where field21 spaned the columns head1 and head2. While now it produces this:

If you want to display a '|' inside a table you can insert its numeric character entity:

||AND|&
||OR ||