Parameters which may be set in free-format headers:

RA       Right Ascension ('hhmmss.sssssss' or 'hh:mm:ss.sssssss')
DEC      Declination ('-ddmmss.ssssss' or '-dd:mm:ss.ssssss')
PMRA     Proper motion in RA direction (mas/yr)
PMDEC    Proper motion in Declination (mas/yr)
PMRV     Radial 'proper motion' (mas/yr)
BETA     Ecliptic latitude (degrees)
LAMBDA   Ecliptic longitude (degrees)
PMBETA   Proper motion in ecliptic latitude (mas/yr)
PMLAMBDA Proper motion in ecliptic longitude (mas/yr)
PX       Parallax (mas)
PEPOCH   Epoch of period/frequency parameters and position (MJD) (not fit)
POSEPOCH Epoch of position (MJD); default is PEPOCH (not fit)
F0       Pulsar rotation frequency (s-2)
F        Alternative for F0
F1       Pulsar rotation frequency derivative (s^-2)
         (if flag 2..9,A..C, fit multiple rotation frequency derivatives)
F2       Pulsar rotation frequency second derivative
Fn       Pulsar rotation frequency n'th derivative;  n=2..9,A..C
P0       Pulsar period (s).  Alternative for 'F0'
P        Alternative for P0
P1       Pulsar period derivative (10^-15).  Alternative for 'F1'
         (if flag>1, fit multiple rotation frequency derivatives)
DM       Dispersion measure (pc cm^-3)
         (if flag 2..9,A, fit n time derivative(s) of DM, n=1..9)	
DMn      n'th time derivative of dispersion measure; n=1..9
DMX_n    DM value in n'th DMX segment (pc cm^-3)
DMX1_n   DM time derivative in n'th DMX segment
DMXEP_n  Epoch of n'th DMX segment (MJD) (not fit)
DMXR1_n  Start date of n'th DMX segment (MJD) (not fit)
DMXR2_n  End date of n'th DMX segment (MJD) (not fit)
A1_n     Projected pulsar semi-major axis of n'th orbit    (n=1,2,3; default 1)
E_n      Eccentricity of n'th orbit                        (n=1,2,3; default 1)
T0_n     Epoch of periastron passage of n'th orbit (MJD)   (n=1,2,3; default 1)
TASC     Epoch of ascending node passage (MJD)
PB_n     Period of n'th orbit (days)                       (n=1,2,3; default 1)
OM_n     Longitude of periastron passage, n'th orbit (deg) (n=1,2,3; default 1)
FB       Frequency of orbit                                (n=10)
FB_n     n'th time derivative of frequency of orbit        (n=10)
FBJ_n    Jump in orbital frequency                         (n=10)
TFBJ_n   Time of n'th jump in orbital frequency            (n=10)
EPS1     First Laplace parameter [eccentricity times sin(omega)]
EPS2     Second Laplace parameter [eccentricity times cos(omega)]
EPS1DOT  Time derivative of EPS1
EPS2DOT  Time derivative of EPS2
OMDOT    Rate of periastron advance (deg/yr) 
OM2DOT   Second time derivative of angle of periastron (rad/s^2)
XOMDOT   Rate of periastron advance minus GR prediction (deg/yr)
PBDOT    Rate of change of orbital period (10^-12) 
XPBDOT   Rate of change of orbital period minus GR prediction (10^-12)
GAMMA    Time dilation & gravitational redshift (s) 
PPNGAMMA PPN parameter gamma
SINI     Sine of inclination angle  
MTOT     Total system mass (solar masses)
M2       Companion mass (solar masses) 
DR       Relativistic deformation of the orbit (not fit)
DTHETA   Relativistic deformation of the orbit (-6) 
XDOT     Rate of change of projted semi-major axis (10^-12 s/s) 
XDOT_1   Alias for XDOT (note different unit convention than XDOT_2, etc.)
XDOT_n   n'th derivative of projected semi-major axis n=2..9 (1/s,1/s^2,etc)
X2DOT    Second time derivative of projected semi-major axis (1/s)
EDOT     Rate of change of eccentricity (-12)
AFAC     aberration geometric factor (sin(eta)/sin(lambda))
A0       aberration parameter (microsec) (not fit)
B0       aberration parameter (microsec) (not fit)
BP       tensor multi-scalar parameter beta-prime (not fit)
BPP      tensor multi-scalar parameter beta-prime-prime (not fit)
GLEP_n   Epoch of glitch n, n=1..9 (MJD) (not fit)
GLPH_n   Glitch n phase increment
GLF0_n   Permanent glitch n pulse frequency increment (s^-1)
GLF1_n   Permanent glitch n frequency derivative increment (s^-2)
GLF0D_n  Decaying glitch n frequency increment (s^-1)
GLTD_n   Decay time constant for glitch n (days)
JUMP_n   Time offset for segment n defined by "JUMP" TOA command
JUMP -f v Tempo2-style flag-based JUMP syntax (f=flag name, v=flag value)