The library can not render some escape codes about positions.

Hi.

I have a tiny test.

The next code puts a text in the bottom of terminal with urwid:

import urwid

def exit_on_q(key):
    if key in ('q', 'Q'):
        raise urwid.ExitMainLoop()


txt = urwid.Text(u"Hello World")
fill = urwid.Filler(txt, 'bottom')
loop = urwid.MainLoop(fill, unhandled_input=exit_on_q)

loop.run()

And it shows in term:

And the code to get the output in other python file is:

import os
import fcntl
import subprocess

p = subprocess.Popen(['python3', '/tmp/test00.py'], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

fd = p.stdout.fileno()  
fl = fcntl.fcntl(fd, fcntl.F_GETFL)  
fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)
fd = p.stderr.fileno()  
fl = fcntl.fcntl(fd, fcntl.F_GETFL)  
fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)
a = p.stdout.read()

from ansi2html import Ansi2HTMLConverter
conv = Ansi2HTMLConverter()
with open('/tmp/caca.html', 'w') as f: 
    f.write(conv.convert(a.decode('utf8')))
a.decode('utf8')

And the output is:

Start by running the provided urwid and ansi2html reproducer, focusing on Ansi2HTMLConverter.convert and how terminal position escape codes are handled. Compare the terminal output with the generated HTML and add a regression test showing the expected positioning behavior.