conditional block display with TBS in DOCX tables - conditional-statements

Question

I am processing DOCX files for invoices with TBS. A first TBS block contains all the taxable items, one per line, followed by lines for subtotal and tax. A second TBS block contains all the non-taxable items, followed by one line for grand total.
I would like to leave out the first block, the subtotal and the tax amount if there are no taxable items.
I also would like to leave the second block out if there are no non-taxable items.
This is the basic structure:
[ItemListTx;block=begin]
[ItemListTx.s] [ItemListTx.a]
[ItemListTx;block=end]
subtotal [abk.tt]
tax [abk.tx]
[ItemListEx;block=begin;enlarge=tbs:p]
[ItemListTx.s] [ItemListTx.a]
[ItemListEx;block=end;enlarge=tbs:p]
total [abk.ttlx]
I wrapped the first five lines into a guarding block with a condition under which to display it:
[onshow;block=begin;enlarge=tbs:p;when 0=1]
...
[onshow;block=end;enlarge=tbs:p]
I did the same for the second block. This works OK. Note that the wrapper block statements are on different lines.
I am still a bit unhappy with the condition though. Is there any other way than setting a flag on the PHP side? It seems to me the second block should do without a wrapper, too.
Note: For editing reasons each item line is a table in itself, really.

Answer 1

Here is how it can easily be done:
| [ItemListTx.s;block=tbs:row;bmagnet=3*tbs:row] | [ItemListTx.a] |
| Subtotal: | [abk.tt] |
| Tax: | [abk.tx] |
| [ItemListEx.s;block=tbs:row;bmagnet=3*tbs:row] | [ItemListEx.a] |
| Total: | [abk.ttlx] |
Explanations:
Parameter bmagnet enabled you to define the block to delete when the data to merge with MergeBlock() are empty.
3*tbs:row means 3 successive table rows.
With OpenTBS it is not recommended to use explicit blocks (block=begin/block=end) because we cannot be sure where they is placed in the inner XML. It is better to use relatives blocks (such as block=tbs:p).