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International
Tables for Crystallography Volume G Definition and exchange of crystallographic data Edited by S. R. Hall and B. McMahon © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. G. ch. 2.3, p. 40
Section 2.3.3.2. Details of the header section
a
Department of Mathematics and Computer Science, Kramer Science Center, Dowling College, Idle Hour Blvd, Oakdale, NY 11769, USA, and bESRF/EMBL Grenoble, 6 rue Jules Horowitz, France |
The start of a header section is delimited by the usual CIF data_ token. Optionally, a header identifier, ###_START_OF_HEADER, may be used before the data_ token, followed by the carriage return, line feed pair, as an aid in debugging, but it is not required. (Naturally, another carriage return, line feed pair should immediately precede this and all other CBF identifiers, with the exception of the CBF file identifier at the very start of the file.) A header section, including the identification items which delimit it, uses only ASCII characters and is divided into `lines'. The `line separator' symbols \r\n (carriage return, line feed) are the same regardless of the operating system on which the file is written. This is an important difference from CIF, but must be so, as the file contains binary data and cannot be translated from one operating system to another, which is the case for ASCII text files. While a properly functioning CBF API should write the full \r\n line separator, it should recognize any of three sequences \r, \n, \r\n as valid line separators so that hand-edited headers will not be rejected.
The header section in a CBF obeys all CIF rules (Chapter 2.2![[link]](/graphics/greenarr.gif)
) with the exception of the line separators, i.e.:
(i) `Lines' are a maximum of 80 characters long. (This will be increased to 2048 in line with the CIF version 1.1 specification.)
(ii) All data names (tags) start with an underscore character `_'.
(iii) The hash symbol `#' (outside a quoted character string) means that all text up to the line separator is a comment.
(iv) White space outside character strings is not significant.
(v) Data names are case-insensitive.
(vi) The data item follows the data-name separator and may be of one of two types: character string (char) or number (numb). The type is specified for each data name.
(vii) Character strings may be delimited with single or double quotes, or blocks of text may be delimited by semicolons occurring as the first character on a line.
(viii) The loop_ mechanism allows a data name to have multiple values. Immediately following the loop_, one or more data names are listed without their values, as column headings. Then one or more rows of values are given.
(ix) Any CIF data name may occur within the header section.
The tokens data_ and loop_ have special meaning in CIF and should not be used except in their indicated places. The tokens save_, stop_ and global_ also have special meaning in CIF's parent language, STAR, and should also not be used.
A single header section may contain one or more data_ blocks.
