I am thinking about adding a feature that would involve getting an account balance based on a filtered set of postings. I came across the account_t::amount method which takes a expr_t parameter. It appears that this expr_t will modify a posting amount before it is added to the account total. However, it does not appear this would jive well with the way the account total is computed, that is, by updating a previously computed account total. So I believe this causes two issues:

1. The account_t::amount method, when called with an expr argument, will not compute the entire account total based on expr. Only postings not included since the most recent call to account_t::amount will reflect expr. This could lead to unexpected results if a user makes use of the expr argument.
2. The amount method could give unexpected results if a previous invocation of account_t::amount used the expr argument as some postings may be factored into the total with the old expr.

Is this intended behavior? Or is there some safeguard to prevent this that I missed? It is difficult for me to know whether this is intended since I cannot find any call to account_t::amount that uses the expr argument.

If the current behavior is not intended, then I believe a fix would be relatively easy: whenever the expr argument exists, recompute the total from scratch and do not affect the totals stored in xdata_->self_details.