Question

I’m looking at the source code of Nokogiri::CSS, because I needed to convert CSS selectors to XPATH. After running a sample code and calling the xpath_for method, I see that it returns an array. Why is this? Are there any chances a CSS selector would return more than one xpath?

[18] pry(main)> Nokogiri::CSS.xpath_for 'div.divddy input:first'
=> ["//div[contains(concat(' ', @class, ' '), ' divddy ')]//input[position() = 1]"]

Answer 1

A CSS selector can contain multiple components separated by commas:

5. Groups of selectors

A comma-separated list of selectors represents the union of all elements selected by each of the individual selectors in the list.

For example:

div.divddy input:first, div#where_is input.pancakes_house { /*...*/ }

So presumably xpath_for returns an array in case you hand it a grouped selector. For example:

>> Nokogiri::CSS.xpath_for 'div.divddy input:first, div#where_is input.pancakes_house'
=> ["//div[contains(concat(' ', @class, ' '), ' divddy ')]//input[position() = 1]", "//div[@id = 'where_is']//input[contains(concat(' ', @class, ' '), ' pancakes_house ')]"]

Note that the returned array has length two in this case.