How do I get scalars from nested yaml structures?

[GrabCAD-Gary]

I've been trying all day to pull the values from keys that have them in a file like this in bash:

# Top comment
block1:
    parameters:
        root:
            # Comment
            rp1: sommat2
            rp2: p212
        level1:
            gp1: sommat2
            gp2: g212
block2:
    parameters:
        test1: val1
        test2: val2
        test3: val3
param1: ps1
param2: pqWx2q641muus3LMHZUMIldTEhvWR4tSpZqWcVnrb48
param3: name
param4:
    - p1
    - p2
    - some value
param5:
    - p1: test
    - p2: some
    - p3: some value

That is, I want to get the keys and values for rp1 and rp2 from block1/root and for gp1 and gp2 from block1/level1, etc. According to the yaml docs that means I want to skip the seqs and map labels and get the scalar vales from inside the maps. I used your snippet to print a comment next to each entry and that says these entries are scalars. I've tried everything from here that looked like it might help and a myriad other things without success. I can get the entries:

# Comment
rp1: sommat2
rp2: p212
gp1: sommat2
gp2: g212

with yq -r '.block1.parameters | to_entries[].value'

but then yq won't split them because it says they're maps or a slew of other reasons, depending on the code. Dumping them shows that the entire string key: value seems to have been grabbed as a key (single value) and not as a key/value pair. My goal is to set some vars based on these keys and values. I've tried the tips and recipes here for getting arrays and setting env. var.s. That doesn't work here apparently because of the nesting. I've tried so many things I've lost track of them all. It appears that this would be achievable if I had just key: value entries at the root level but I can't get the nested pairs. This is as close as I've got. Could someone please show me how to do this?

I should point out that the contents of such a file will be unknown so I'm looking to iterate and find the right entries without knowledge of the keys. In case that wasn't obvious Pulling a single entry by name or all entries I can do.

Also, if you could point me to some docs that explain the notation for dots, double dots, brackets, etc. that'd help immensely. I can't find any explanation of those things here anywhere. The operator docs use them but there's no explanation that I can find.

Thanks.