In terms of the documentation quality I do agree that it's documented but not obviously, you mentioned that it's in the "SQL Functions Returning Sets" section however this section isn't indicated to by the Array functions and operators page - additionally while, if you know that you're dealing with an issue related to SRFs it's pretty easy to find - attempting to get at that information via google isn't going to get you anything unless you specifically hone in on set returning functions. I ended up finding that doc page after finding a SO answer that mentioned SRFs while searching for "postgres unnest cartesian product".
The information is in the documentation, but the documentation isn't always super good at linking to other relevant portions of the documentation and, honestly, reading the documentation about the feature you need is reasonable, but I don't expect most people are reading the full postgres docs before starting to play around with it. So I don't disagree that the information is there, but I do think it is mostly inaccessible due to the structure of the documentation.
In terms of the documentation quality I do agree that it's documented but not obviously, you mentioned that it's in the "SQL Functions Returning Sets" section however this section isn't indicated to by the Array functions and operators page - additionally while, if you know that you're dealing with an issue related to SRFs it's pretty easy to find - attempting to get at that information via google isn't going to get you anything unless you specifically hone in on set returning functions. I ended up finding that doc page after finding a SO answer that mentioned SRFs while searching for "postgres unnest cartesian product".
The information is in the documentation, but the documentation isn't always super good at linking to other relevant portions of the documentation and, honestly, reading the documentation about the feature you need is reasonable, but I don't expect most people are reading the full postgres docs before starting to play around with it. So I don't disagree that the information is there, but I do think it is mostly inaccessible due to the structure of the documentation.