Add references to names documentation

[quinnj]

I wanted to brush up on the various "selection" options for a DataFrame. I conveniently found a section about the names function in the "Getting Started" page of the manual/docs. And clicking into the reference docs for names provided a fair amount of details, particularly with some good examples of using function selectors. But I felt a bit lots with:

any column selector (Symbol, string or integer; :, Cols, All, Between, Not, a regular expression, or a vector of Symbols, strings or integers)

i.e. it wasn't clear to me what Cols or All are, and how to use them. And no (@ref) links to follow to learn more.

I did eventually find the helpful Indexing page which had more information, so maybe the request here is to save the next person some random clicking around and just link to the Indexing page from the names docs? Thoughts?

[bkamins]

@mortenpi - your advice on Documenter.jl would be welcome here. We have two issues (I ask about MWE, as the rest follows naturally):

• Cols is defined in DataAPI.jl, how can we robustly make a cross-reference in a docstring of some function to this definition from DataFrames.jl documentation?
• How can we robustly add a cross-reference in a docstring of some function to some page in the manual? (this is within the same package, DataFrames.jl in this case)

(in the whole process I am mostly concerned that hardcoding URLs is not a good solution)

I ask because https://juliadocs.github.io/Documenter.jl/stable/man/guide/#Cross-Referencing describes only cross-referencing within documentation. Thank you!

[mortenpi]

Cross-references to other packages must be done by putting the URL in manually unfortunately (JuliaDocs/Documenter.jl#688).

However, to reference a page/section, you should be able to just do [Section Title](@ref) as usual, even if the reference is in a docstring (or, in 0.28, you'll be able to even do [some other text](@ref "Section Title"); JuliaDocs/Documenter.jl#1900).

[bkamins]

OK - I know what to do then. Thank you!