On the QWeb developer documentation says that we can log some javascript values with:

<t t-set="foo" t-value="42"/>
<t t-log="foo"/>

I'm trying to log a variable decoded from JSON on an invoice report

(http://local.odoo/report/html/account.report_invoice/$ID) and I get nothing:

<t t-set="payments_lines" t-value="json.loads(o.payments_widget)"/>
<t t-log="o.payments_widget"/>

t-log is not logging anything as I'm trying to use it with another invoice line var:

<tr t-foreach="o.invoice_line_ids" t-as="l" class="bg-esecondary">
    <t t-log="l.name"/>
    ...

I have odoo.conf with:

dev_mode = True
auto_reload = True

and my service is starting with --dev all, with no joy
where's applicable to use it?

I'm missing something? :(