How to use regular expression for a mini markup mechanism in PDF reports?

Question

I want to build a mini markup mechanism for PDF reports in Odoo 17. How can I use regular expression in Qweb report to change the output?

I want to create a bold text string from **a bold text string**

For that I use

<td name="td_name"><span t-esc="o.minimarkupmagic(line.name)">Bacon Burger</span></td>

in my template. In my model (which I inherit from sale.order) I define a method

def minimarkupmagic(self,txt):
    ​txt = re.sub(r'\*{2,2}(.*?)\*{2,2}', r'\1', txt)
    ​txt = re.sub(r'_{2,2}(.*?)_{2,2}', r'\1', txt)
    ​txtArr = txt.split('\n')
    ​txt = '<br/>'.join(txtArr)
    ​return txt

and send it to my template within

docargs = {
    ...,
    ​'minimarkupmagic': self.minimarkupmagic
}

from def render_html().

It works half way: I only get an output like

<span class="bold">a bold text string</span>

in my report, so it seems that the method runs after the rendering of the HTML to PDF.

So how could I get my HTML get interpreted earlier and get my correct output?

Thanks!