I use bash 4.4.12(1)-release (version reported by bash itself). Version reported by my distro (debian): 4.4-5.

When I type "help" into "bash" I see this:

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GNU bash, version 4.4.12(1)-release (x86_64-pc-linux-gnu)
These shell commands are defined internally.  Type `help' to see this list.
Type `help name' to find out more about the function `name'.
Use `info bash' to find out more about the shell in general.
Use `man -k' or `info' to find out more about commands not in this list.

A star (*) next to a name means that the command is disabled.

 job_spec [&]                                                       history [-c] [-d offset] [n] or history -anrw [filename] or his>
 (( expression ))                                                   if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ]..>
 . filename [arguments]                                             jobs [-lnprs] [jobspec ...] or jobs -x command [args]
 :                                                                  kill [-s sigspec | -n signum | -sigspec] pid | jobspec ... or k>
 [ arg... ]                                                         let arg [arg ...]
 [[ expression ]]                                                   local [option] name[=value] ...
 alias [-p] [name[=value] ... ]                                     logout [n]
 bg [job_spec ...]                                                  mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u f>
 bind [-lpsvPSVX] [-m keymap] [-f filename] [-q name] [-u name] [>  popd [-n] [+N | -N]
 break [n]                                                          printf [-v var] format [arguments]
 builtin [shell-builtin [arg ...]]                                  pushd [-n] [+N | -N | dir]
 caller [expr]                                                      pwd [-LP]
 case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... esac         read [-ers] [-a array] [-d delim] [-i text] [-n nchars] [-N nch>
 cd [-L|[-P [-e]] [-@]] [dir]                                       readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C ca>
 command [-pVv] command [arg ...]                                   readonly [-aAf] [name[=value] ...] or readonly -p
 compgen [-abcdefgjksuv] [-o option] [-A action] [-G globpat] [-W>  return [n]
 complete [-abcdefgjksuv] [-pr] [-DE] [-o option] [-A action] [-G>  select NAME [in WORDS ... ;] do COMMANDS; done
 compopt [-o|+o option] [-DE] [name ...]                            set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...]
 continue [n]                                                       shift [n]
 coproc [NAME] command [redirections]                               shopt [-pqsu] [-o] [optname ...]
 declare [-aAfFgilnrtux] [-p] [name[=value] ...]                    source filename [arguments]
 dirs [-clpv] [+N] [-N]                                             suspend [-f]
 disown [-h] [-ar] [jobspec ... | pid ...]                          test [expr]
 echo [-neE] [arg ...]                                              time [-p] pipeline
 enable [-a] [-dnps] [-f filename] [name ...]                       times
 eval [arg ...]                                                     trap [-lp] [[arg] signal_spec ...]
 exec [-cl] [-a name] [command [arguments ...]] [redirection ...>   true
 exit [n]                                                           type [-afptP] name [name ...]
 export [-fn] [name[=value] ...] or export -p                       typeset [-aAfFgilnrtux] [-p] name[=value] ...
 false                                                              ulimit [-SHabcdefiklmnpqrstuvxPT] [limit]
 fc [-e ename] [-lnr] [first] [last] or fc -s [pat=rep] [command>   umask [-p] [-S] [mode]
 fg [job_spec]                                                      unalias [-a] name [name ...]
 for NAME [in WORDS ... ] ; do COMMANDS; done                       unset [-f] [-v] [-n] [name ...]
 for (( exp1; exp2; exp3 )); do COMMANDS; done                      until COMMANDS; do COMMANDS; done
 function name { COMMANDS ; } or name () { COMMANDS ; }             variables - Names and meanings of some shell variables
 getopts optstring name [arg]                                       wait [-n] [id ...]
 hash [-lr] [-p pathname] [-dt] [name ...]                          while COMMANDS; do COMMANDS; done
 help [-dms] [pattern ...]                                          { COMMANDS ; }
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It seems that everything in this list is shell builtins and grammar constructions. Infortunately, this is not true. "variables" is not shell builtin. When I type "variables", I simply get "command not found". So "variables" got included in the list simply because it is help topic. So, please write about "variables" separately", for example, write it the end of list 'Also, you can see help on bash variables using "help variables"'. So, please double-check that all listed commands are really builtins (and bash syntactic constructions).

How I came to this? Well, I am developing very portable shell script not limited to bash. I need to know what builtins are always available to it. To do this, I took a list of shell builtins from different shells and tried to perform set-theoretic intersection of it. But then I suddenly noticed, that "variables" listed in list of bash builtins is not true builtin. You confused me.