This email came into the Gepsio inbox recently:
I’ve been playing around with the library. My first exercise for myself is trying to reconstruct the financial statements. I thought I’d group Facts by time periods. The ContextRefNames were not what I expected. There were overlaps in names like FD2015XXX, D2015XXX, I2015XXX. Do you know the difference between the prefixes? I’m using Whole Foods https://www.sec.gov/Archives/edgar/data/865436/000086543615000177/0000865436-15-000177-index.htm
Is there a particular convention that the contextrefnames follow? I had a look at Walmart and they use a similar, but different convention.
Unfortunately, the answer is “no”.
Context IDs and references have no meaning. They are syntax, not semantics. Context reference names are arbitrary and have meaning only to link items within the individual document instances.
Section 4.7.1 of the XBRL 2.1 specification discusses the “id” attribute of a <context> element:
Every <context> element MUST include the @id attribute. The content of the @id attribute MUST conform to the [XML] rules for attributes with the ID type (http://www.w3.org/TR/REC-xml#NT-TokenizedType). The @id attribute identifies the context (see Section 4.7) so that it may be referenced by item elements.
The specification does not impose any semantics on the contents of the ID attribute.