Markdown not escaping MD special characters

[exiva]

Error details
When using markdown in fpdf2 it should respect escaped characters like underscores and asterisks. It does not currently.

Minimal code
Please include some minimal Python code reproducing your issue:

from fpdf import FPDF

pdf = FPDF(format=(101.6, 152.4))
pdf.set_margin(2)
pdf.add_page()
pdf.set_font("Times", size=16)

txt = "**This** is a markdown test. Theres\__double underscores"
pdf.multi_cell(w=50, text=txt, align='L', new_x='RIGHT',
                new_y='TOP', border=0, markdown=True,)

pdf.output("md.pdf")

Should output "This is a markdown test. Theres__double underscores" but outputs

Environment
Please provide the following information:

• Operating System: macOS 14.5 Apple Silicon M2 Mac Mini
• Python version: 3.11.9
• fpdf2 version used: 2.7.9

[gmischler]

Thanks for reporting this, and welcome to fpdf2, @exiva !

Well, the documentation doesn't promise that our markup parser would honor backslash escapes, so technically this isn't a bug... 😉

it is a perfectly valid feature request, though!
Any chance you might want to submit a PR?

[andersonhc]

If you want a head start, markdown markers are handled on fpdf _parse_chars() function.

fpdf2/fpdf/fpdf.py

Lines 3500 to 3515 in d574b07

	if markdown:
	if (
	is_marker
	and (not txt_frag or txt_frag[-1] != half_marker)
	and (len(text) < 3 or text[2] != half_marker)
	):
	if txt_frag:
	yield frag()
	if text[:2] == self.MARKDOWN_BOLD_MARKER:
	in_bold = not in_bold
	if text[:2] == self.MARKDOWN_ITALICS_MARKER:
	in_italics = not in_italics
	if text[:2] == self.MARKDOWN_UNDERLINE_MARKER:
	in_underline = not in_underline
	text = text[2:]
	continue

[gmischler]

Implemented in #1224

[Lucas-C]

Hi.

I'd like to reopen this issue to further discuss this.

I may be mistaken, but the escaping implemented in PR #1224 does not seem to conform to the CommonMark standard.

You can test the rendering of \\**Lorem\\** \\\\__Ipsum\\\\__ --dolor-- in https://spec.commonmark.org/dingus/

The result is this:

Escaping double underscores in Markdown should be done this way:
\_\_Ipsum\_\_

What do you think @gmischler, @exiva & @david-fed?