Sustainability of Digital Formats: Planning for Library of Congress Collections

The Strict variant of XLSX disallows a variety of elements and attributes that are permitted in the more common Transitional variant (XLSX/OOXML_2012). The markup for the Strict variant is essentially a subset of markup for the Transitional variant, but the schemas use different namespaces and are distributed separately in complete form.

The Strict variant of XLSX described here was introduced during the standardization in ISO/IEC 29500 in 2008 with the intention of excluding features included in ECMA-376, Edition 1 that were present simply to handle bugs and features of earlier spreadsheet applications. The intent of the split of the markup specification into Strict (Part 1) and Transitional (Part 4) was that applications would create new documents in the Strict variant; however, in practice, pressure for backwards compatibility has meant that most new files are marked up by applications using the Transitional namespace even if they use no features that are incompatible with the Strict specification.

Among the key differences between the Strict variant and the Transitional variant are:

• Use of VML (Vector Markup Language) for graphics is not permitted in XLSX Strict. All graphics, for example in charts, are represented using DrawingML.
• Characters in XLSX Strict are based on UNICODE. Other character sets and codepage technologies are not permitted.
• To comply with XLSX Strict, elements and attributes with deprecated names that use "left" and "right" in relation to start and end of text must be replaced by substitutes that are neutral in relation to the direction of text.
• Legacy techniques for protecting workbooks and their contents are disallowed in XLSX Strict.
• XLSX Strict has a value type for cells of date, using the Complete, Extended Format Calendar representations in ISO 8601. For reasons of backwards compatibility, this typed use of ISO 8601 dates is not permitted in XLSX Transitional. See Notes below.
• XLSX Strict does not permit the use of representations for drawing elements and attributes where percentages used to specify scaling and positioning are represented as integers outside the range 0-100. This technique was formerly used for performance reasons.

For discussion of other aspects of the Strict XLSX format, see the description of the more common Transitional variant of XLSX, XLSX/OOXML_2012.