A line beginning with 'loop_' is repeated until the corresponding loop in the CIF file is exhausted; all the CIF items in the line must be in the same loop in the CIF input file. All CIF data names and the string 'loop_' must be given as lower case in the format file; in the CIF input file the standard CIF rules apply.
A line containing at least 4 consecutive underscores is copied to the output file unchanged, and may be used for drawing a horizontal line. There are also two pseudo-CIF-identifies: '_tabno' is the number of the table, and '_comno' is a number to identify the compound. Both may be set via the CIFTAB menu. '_tabno' but not '_comno' is incremented each time it is used.
An underscore '_' followed by a space may be used to continue on the next line without creating a new line in the output file. Lines beginning with question marks are output to the console (without the leading question mark) as questions; if the answer to the question is not 'Y' or 'y', everything in the format file is skipped until the next line which begins with a question mark. Lines beginning with a dollar '$' are not interpreted as text, but are scanned for the following strings (upper or lower case, quotes not essential):
'xtext': output should be formatted for the Siemens SHELXTL xtext program. 'xtext,deutsch': as above, but translated into German.The above directive, if present, should be the first line of the format file.
The directive $symops:n, where n is an integer, prints the symmetry operations used to generate equivalent atoms, starting each line of text in column n. These operators are references by '#m' (where m is an integer) after the atom name. The line beginning '$symops:n' usually follows the table of selected bond lengths and angles, but could also be used for a torsion angles table.
The remaining directives may appear at any point in the format file except immediately after a continuation line marker, but always on a line beginning with '$'.
'h=none': leave out all hydrogen atoms. 'h=only': leave out all non-hydrogen atoms. 'h=free': leave out riding or rigid group hydrogens but include the rest. 'h=all': include all hydrogen and all other atoms.The hydrogen atom directives apply only to coordinates tables; hydrogen atoms are recognised by the .._type_symbol 'H'. The publication flags can be used to control which hydrogen atoms appear in tables of bond lengths, angles etc.
'brack': Atom names should include brackets (if present in the CIF file) 'nobrack': Brackets are deleted from the atom names. 'flag': Only output items for which the publication flag is 'Y' or 'y' 'noflag': Output all items, ignoring the publication flag.The default settings are '$h=none,brack,flag'. The standard tables file 'ciftab.def' illustrates the use of most of these facilities. CIF_TABLES extends some of the standard CIF codes to make them more suitable for tables, and also takes special action when items such as _refine_ls_extinction_coef are missing or undefined.