Section 207: The command codes
Before we can go any further, we need to define symbolic names for the internal code numbers that represent the various commands obeyed by .
These codes are somewhat arbitrary, but not completely so.
For example, the command codes for character types are fixed by the language, since a user says, e.g., ‘\catcode `\$ = 3’ make $ a math delimiter, and the command code MATH_SHIFT is equal to 3.
Some other codes have been made adjacent so that case statements in the program need not consider cases that are widely spaced, or so that case statements can be replaced by if statements.
At any rate, here is the list, for future reference. First come the “catcode” commands, several of which share their numeric codes with ordinary commands when the catcode cannot emerge from ’s scanning routine.
constants.h
#define ESCAPE 0 // escape delimiter (called \ in The TeXbook)
#define RELAX 0 // do nothing (\relax)
#define LEFT_BRACE 1 // beginning of a group ({)
#define RIGHT_BRACE 2 // ending of a group (})
#define MATH_SHIFT 3 // mathematics shift character ($)
#define TAB_MARK 4 // alignment delimiter (&, \span)
#define CAR_RET 5 // end of line (CARRIAGE_RETURN, \cr, \crcr)
#define OUT_PARAM 5 // output a macro parameter
#define MAC_PARAM 6 // macro parameter symbol (#)
#define SUP_MARK 7 // superscript (^)
#define SUB_MARK 8 // subscript (_)
#define IGNORE 9 // characters to ignore (^^@)
#define ENDV 9 // end of <v_j> list in alignment template
#define SPACER 10 // characters equivalent to blank space ( )
#define LETTER 11 // characters regarded as letters (A..Z, a..z})
#define OTHER_CHAR 12 // none of the special character types
#define ACTIVE_CHAR 13 // characters that invoke macros (~)
#define PAR_END 13 // end of paragraph (\par)
#define MATCH 13 // match a macro parameter
#define COMMENT 14 // characters that introduce comments (%)
#define END_MATCH 14 // end of parameters to macro
#define STOP 14 // end of job (\end, \dump)
#define INVALID_CHAR 15 // characters that shouldn't appear (^^?)
#define DELIM_NUM 15 // specify delimiter numerically (\delimiter)
#define MAX_CHAR_CODE 15 // largest catcode for individual characters
Section 208
Next are the ordinary run-of-the-mill command codes.
Codes that are MIN_INTERNAL or more represent internal quantities that might be expanded by ‘\the’.
constants.h
#define CHAR_NUM 16 // character specified numerically (\char)
#define MATH_CHAR_NUM 17 // explicit math code (\mathchar)
#define MARK 18 // mark definition (\mark)
#define XRAY 19 // peek inside of TeX (\show, \showbox, etc.)
#define MAKE_BOX 20 // make a box (\box, \copy, \hbox, etc.)
#define HMOVE 21 // horizontal motion (\moveleft, \moveright)
#define VMOVE 22 // vertical motion (\raise, \lower)
#define UN_HBOX 23 // unglue a box (\unhbox, \unhcopy)
#define UN_VBOX 24 // unglue a box (\unvbox, \unvcopy)
#define REMOVE_ITEM 25 // nullify last item (\unpenalty, \unkern, \unskip)
#define HSKIP 26 // horizontal glue (\hskip, \hfil, etc.)
#define VSKIP 27 // vertical glue (\vskip, \vfil, etc.)
#define MSKIP 28 // math glue (\mskip)
#define KERN 29 // fixed space (\kern)
#define MKERN 30 // math kern (\mkern)
#define LEADER_SHIP 31 // use a box (\shipout, \leaders, etc.)
#define HALIGN 32 // horizontal table alignment (\halign)
#define VALIGN 33 // vertical table alignment (\valign)
#define NO_ALIGN 34 // temporary escape from alignment (\noalign)
#define VRULE 35 // vertical rule (\vrule)
#define HRULE 36 // horizontal rule (\hrule)
#define INSERT 37 // vlist inserted in box (\insert)
#define VADJUST 38 // vlist inserted in enclosing paragraph (\vadjust)
#define IGNORE_SPACES 39 // gobble |spacer| tokens (\ignorespaces)
#define AFTER_ASSIGNMENT 40 // save till assignment is done (\afterassignment)
#define AFTER_GROUP 41 // save till group is done (\aftergroup)
#define BREAK_PENALTY 42 // additional badness (\penalty)
#define START_PAR 43 // begin paragraph (\indent, \noindent)
#define ITAL_CORR 44 // italic correction (\/)
#define ACCENT 45 // attach accent in text (\accent)
#define MATH_ACCENT 46 // attach accent in math (\mathaccent)
#define DISCRETIONARY 47 // discretionary texts (\-, \discretionary)
#define EQ_NO 48 // equation number (\eqno, \leqno)
#define LEFT_RIGHT 49 // variable delimiter (\left, \right)
#define MATH_COMP 50 // component of formula (\mathbin, etc.)
#define LIMIT_SWITCH 51 // diddle limit conventions (\displaylimits, etc.)
#define ABOVE 52 // generalized fraction (\above, \atop, etc.)
#define MATH_STYLE 53 // style specification (\displaystyle, etc.)
#define MATH_CHOICE 54 // choice specification (\mathchoice)
#define NON_SCRIPT 55 // conditional math glue (\nonscript)
#define VCENTER 56 // vertically center a vbox (\vcenter)
#define CASE_SHIFT 57 // force specific case (\lowercase, \uppercase)
#define MESSAGE 58 // send to user (\message, \errmessage)
#define EXTENSION 59 // extensions to \TeX\ (\write, \special, etc.)
#define IN_STREAM 60 // files for reading (\openin, \closein)
#define BEGIN_GROUP 61 // begin local grouping (\begingroup)
#define END_GROUP 62 // end local grouping (\endgroup)
#define OMIT 63 // omit alignment template (\omit)
#define EX_SPACE 64 // explicit space (\ )
#define NO_BOUNDARY 65 // suppress boundary ligatures (\noboundary)
#define RADICAL 66 // square root and similar signs (\radical)
#define END_CS_NAME 67 // end control sequence (\endcsname)
#define MIN_INTERNAL 68 // the smallest code that can follow \the
#define CHAR_GIVEN 68 // character code defined by \chardef
#define MATH_GIVEN 69 // math code defined by \mathchardef
#define LAST_ITEM 70 // most recent item (\lastpenalty, \lastkern, \lastskip)
#define MAX_NON_PREFIXED_COMMAND 70 // largest command code that can't be \global
Section 209
The next codes are special; they all relate to mode-independent assignment of values to ’s internal registers or tables.
Codes that are MAX_INTERNAL or less represent internal quantities that might be expanded by ‘\the’.
constants.h
#define TOKS_REGISTER 71 // token list register (\toks)
#define ASSIGN_TOKS 72 // special token list (\output, \everypar, etc.)
#define ASSIGN_INT 73 // user-defined integer (\tolerance, \day, etc.)
#define ASSIGN_DIMEN 74 // user-defined length (\hsize, etc.)
#define ASSIGN_GLUE 75 // user-defined glue (\baselineskip, etc.)
#define ASSIGN_MU_GLUE 76 // user-defined muglue (\thinmuskip, etc.)
#define ASSIGN_FONT_DIMEN 77 // user-defined font dimension (\fontdimen)
#define ASSIGN_FONT_INT 78 // user-defined font integer (\hyphenchar, \skewchar)
#define SET_AUX 79 // specify state info (\spacefactor, \prevdepth)
#define SET_PREV_GRAF 80 // specify state info (\prevgraf)
#define SET_PAGE_DIMEN 81 // specify state info (\pagegoal, etc.)
#define SET_PAGE_INT 82 // specify state info (\deadcycles, \insertpenalties)
#define SET_BOX_DIMEN 83 // change dimension of box (\wd, \ht, \dp)
#define SET_SHAPE 84 // specify fancy paragraph shape (\parshape)
#define DEF_CODE 85 // define a character code (\catcode, etc.)
#define DEF_FAMILY 86 // declare math fonts (\textfont, etc.)
#define SET_FONT 87 // set current font (font identifiers)
#define DEF_FONT 88 // define a font file (\font)
#define REGISTER 89 // internal register (\count, \dimen, etc.)
#define MAX_INTERNAL 89 // the largest code that can follow \the
#define ADVANCE 90 // advance a register or parameter (\advance)
#define MULTIPLY 91 // multiply a register or parameter (\multiply)
#define DIVIDE 92 // divide a register or parameter (\divide)
#define PREFIX 93 // qualify a definition (\global, \long, \outer)
#define LET 94 // assign a command code (\let, \futurelet)
#define SHORTHAND_DEF 95 // code definition (\chardef, \countdef, etc.)
#define READ_TO_CS 96 // read into a control sequence (\read)
#define DEF 97 // macro definition (\def, \gdef, \xdef, \edef)
#define SET_BOX 98 // set a box (\setbox)
#define HYPH_DATA 99 // hyphenation data (\hyphenation, \patterns)
#define SET_INTERACTION 100 // define level of interaction (\batchmode, etc.)
#define MAX_COMMAND 100 // the largest command code seen at |big_switch|
Section 210
The remaining command codes are extra special, since they cannot get through ’s scanner to the main control routine. They have been given values higher than MAX_COMMAND so that their special nature is easily discernible. The “expandable” commands come first.
constants.h
#define UNDEFINED_CS (MAX_COMMAND + 1) // initial state of most |eq_type| fields
#define EXPAND_AFTER (MAX_COMMAND + 2) // special expansion (\expandafter)
#define NO_EXPAND (MAX_COMMAND + 3) // special nonexpansion (\noexpand)
#define INPUT (MAX_COMMAND + 4) // input a source file (\input, \endinput)
#define IF_TEST (MAX_COMMAND + 5) // conditional text (\if, \ifcase, etc.)
#define FI_OR_ELSE (MAX_COMMAND + 6) // delimiters for conditionals (\else, etc.)
#define CS_NAME (MAX_COMMAND + 7) // make a control sequence from tokens (\csname)
#define CONVERT (MAX_COMMAND + 8) // convert to text (\number, \string, etc.)
#define THE (MAX_COMMAND + 9) // expand an internal quantity (\the)
#define TOP_BOT_MARK (MAX_COMMAND + 10) // inserted mark (\topmark, etc.)
#define CALL (MAX_COMMAND + 11) // non-long, non-outer control sequence
#define LONG_CALL (MAX_COMMAND + 12) // long, non-outer control sequence
#define OUTER_CALL (MAX_COMMAND + 13) // non-long, outer control sequence
#define LONG_OUTER_CALL (MAX_COMMAND + 14) // long, outer control sequence
#define END_TEMPLATE (MAX_COMMAND + 15) // end of an alignment template
#define DONT_EXPAND (MAX_COMMAND + 16) // the following token was marked by \noexpand
#define GLUE_REF (MAX_COMMAND + 17) // the equivalent points to a glue specification
#define SHAPE_REF (MAX_COMMAND + 18) // the equivalent points to a parshape specification
#define BOX_REF (MAX_COMMAND + 19) // the equivalent points to a box node, or is |null|
#define DATA (MAX_COMMAND + 20) // the equivalent is simply a halfword number