The source code contains documentation in *roff format using the BSD mdoc macropackage. If your system cannot deal with that, for example because it only has the man macropackage (deprecated) or uses mdocml (which lacks support for the *roff language), you can get preformatted manual pages in catman, XHTML, PDF, and plaintext format from ../../../cats/mir/mksh/ or: https://www.mirbsd.org/MirOS/cats/mir/mksh/