The MathML Operator dictionary gives the suggested dictionary of
rendering properties for operators, fences, separators, and accents in
MathML, all of which are represented by <mo> elements.
In earlier versions of MathML, the operator dictionary was implementation dependent with the values given in the Recommendation text being non normative suggestions. In [[MathML-Core]] the values given are Normative for web platform implementations implementing Core, so in MathML4 it is strongly recommended that these spacing values are used even for non-core implementations to ensure compatibility with renderings of MathML on the web. Conversely some attributes contained in the dictionary are not used by MathML Core level 1 and not listed in the Core document, but are listed in the presentation in MathML 4.
The data for the dictionary presented in both [[MathML-Core]] and
[[MathML4]] is extracted from the
unicode.xml
file which is maintained as part of the sources for [[Entities]]. If you need
to process the information programmatically, you may find processing
unicode.xml directly may be more convenient than the human-oriented
presentations in the Recommendation documents.