(md/security)=

Security

Many people don't understand that markdown format does not care much about security. In many cases you have to pass output to sanitizers. markdown-it provides 2 possible strategies to produce safe output:

Don‘t enable HTML. Extend markup features with plugins. We think it’s the best choice and use it by default.
- That's ok for 99% of user needs.
- Output will be safe without sanitizer.
Enable HTML and use external sanitizer package(s).

Also by default markdown-it prohibits some kind of links, which could be used for XSS:

javascript:, vbscript:
file:
data:, except some images (gif/png/jpeg/webp).

So, by default markdown-it should be safe. We care about it.

If you find a security problem - contact us via executablebooks@gmail.com. Such reports are fixed with top priority.

Plugins

Usually, plugins operate with tokenized content, and that's enough to provide safe output.

But there is one non-evident case you should know - don't allow plugins to generate arbitrary element id and name. If those depend on user input - always add prefixes to avoid DOM clobbering. See discussion for details.

So, if you decide to use plugins that add extended class syntax or autogenerating header anchors - be careful.

(md/performance)=

Performance

You can view our continuous integration benchmarking analysis at: https://executablebooks.github.io/markdown-it-py/dev/bench/, or you can run it for yourself within the repository:

$ tox -e py38-bench-packages -- --benchmark-columns mean,stddev

Name (time in ms)             Mean             StdDev
---------------------------------------------------------------
test_mistune               70.3272 (1.0)       0.7978 (1.0)
test_mistletoe            116.0919 (1.65)      6.2870 (7.88)
test_markdown_it_py       152.9022 (2.17)      4.2988 (5.39)
test_commonmark_py        326.9506 (4.65)     15.8084 (19.81)
test_pymarkdown           368.2712 (5.24)      7.5906 (9.51)
test_pymarkdown_extra     640.4913 (9.11)     15.1769 (19.02)
test_panflute             678.3547 (9.65)      9.4622 (11.86)
---------------------------------------------------------------

As you can see, markdown-it-py doesn‘t pay with speed for it’s flexibility.

`mistune` is not CommonMark compliant, which is what allows for its
faster parsing, at the expense of issues, for example, with nested inline parsing.
See [mistletoes's explanation](https://github.com/miyuchina/mistletoe/blob/master/performance.md)
for further details.