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2nd chunk of `chmod.man`
97885757978ac76fb70aecaff45160c72403241536479e8e000000010000086c
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       A numeric mode is from one to four octal digits (0-7), derived by adding up the bits with values 4, 2, and 1.  Omitted digits are assumed to be leading zeros.  The first digit selects the set user ID (4) and set group
       ID (2) and restricted deletion or sticky (1) attributes.  The second digit selects permissions for the user who owns the file: read (4), write (2), and execute (1); the third selects permissions for other users in the
       file’s group, with the same values; and the fourth for other users not in the file’s group, with the same values.

       chmod never changes the permissions of symbolic links; the chmod system call cannot change their permissions.  This is not a problem since the permissions of symbolic links are never used.  However, for each  symbolic
       link listed on the command line, chmod changes the permissions of the pointed‐to file.  In contrast, chmod ignores symbolic links encountered during recursive directory traversals.

SETUID AND SETGID BITS
       chmod  clears the set‐group‐ID bit of a regular file if the file’s group ID does not match the user’s effective group ID or one of the user’s supplementary group IDs, unless the user has appropriate privileges.  Addi‐
       tional restrictions may cause the set‐user‐ID and set‐group‐ID bits of MODE or RFILE to be ignored.  This behavior depends on the policy and functionality of the underlying chmod system call.  When in doubt, check the
       underlying system behavior.

       For directories chmod preserves set‐user‐ID and set‐group‐ID bits unless you explicitly specify otherwise.  You can set or clear the bits with symbolic modes like u+s and g-s.  To clear these bits for directories with
       a numeric mode requires an additional leading zero like 00755, leading minus like -6000, or leading equals like =755.

RESTRICTED DELETION FLAG OR STICKY BIT
       The restricted deletion flag or sticky bit is a single bit, whose interpretation depends on the file type.  For directories, it prevents unprivileged users from removing or renaming a file in the directory unless
Title: chmod: Numeric Modes, Symbolic Links, and Special Bits
Summary
This section explains how chmod handles numeric modes, symbolic links, and special bits like SETUID, SETGID, and the sticky bit. Numeric modes use octal digits to set permissions, with each digit representing permissions for user, group, and others. Chmod doesn't directly change symbolic link permissions but modifies the target file. The SETUID and SETGID bits are cleared under certain conditions. For directories, chmod preserves these bits unless explicitly changed. The sticky bit prevents unprivileged users from deleting or renaming files in a directory they don't own.