Ilya/Emilia Kabakov : where is our place? (OCLC #52694167)
Just as 041 and 043 can use codes to summarize language and geography data respectively, 045 can summarize the time period of the content.
When 045 has a blank first indicator, the field has only a subfield a which contains a four-character time period code: the first two characters are for the earliest period covered, the last two are for the latest period covered. The codes may be found on the OCLC BibFormats page for 045. The code may represent a much more specific period than what is found in the subject headings.
The code for the century 1900-1999 is ‘x’. A digit may be added to this to represent the decade, so x4 = 1940s. If no digit is used to add specificity, a ’-’ is used, so ‘x-’ is still the range 1900-1999.
045 __ ǂa x4x-