
SHELX file definition

- continuation lines ... =
  ... C. end with a '=' and the next line starts with one or more spaces ' '

- Comments: start with space ' ', rest is ignored

- all characters following '!' or '=' are ignored
  thus we can do 
  if "=" in line:
    line = line.split("=")[0]

- TIME and MOLE are deprecated

- +filename incudes an input file with further instructions until 
  an END instruction is encountered in that file.
  The input from an include is not echoed to the res and lst file 
  It can be used for FRAG and FEND and respective restraints

- The .ins file should always start with 
  TITL
  CELL
  ZERR
  [LATT]
  SYMM
  [NEUT]
  SFAC,
  [DISP]
  UNIT 
  in that order and finish with 
  HKLF and 
  END. 
  Instructions in square brackets
  are not always required. 
  There may be more than one SYMM, SFAC and DISP instructions.
  
- Atom instructions begin with an atom name 
  (up to 4 characters, of which the first must be a letter) 
  (A number is not required)
  X = Letter, Y = number
  X[XXX](0-3)[YYY](0-3)
  
  that do not correspond to any of the SHELXL instructions, 
  and terminated by at least one blank) 
  followed by a scattering factor number [which refers to the list defined by the SFAC instruction(s)], 
  x, y, and z in fractional coordinates, and (optionally) a site occupation factor
  (s.o.f.) and an isotropic U or six anisotropic Uij components (in Angström^2).
  
  XY Y x y z [11.0] [U] or [Uij]
 
  atomname sfac x y z sof[11] U[0.05] or U11 U22 U33 U23 U13 U12
  
  The combination of atom name, PART and RESI numbers must be unique. 

  To fix any atom parameter, add 10.
  
  If any atom parameter is given as (10*m+p), where abs(p) is less than 5 and m is an integer, it
  is interpreted as p*fv_m, where fv_m is the mth free variable (see FVAR). 
  
  
 
 
 
