Can I make options dialog using code?

[Basil2]

I need to create window with several checkboxes (like PowerAuras options dialog but simplier). I expected to do this using CreateFrame(), but the following code doesn't work at all:

function OpenSettingsFrame()
    local f = RecommendOptionsFrame -- this frame is defined in xml file
    f:Show()
    
    CreateFeatureLine(f, RcmSettings.Riptide)
    CreateFeatureLine(f, RcmSettings.Surge)
end

function CreateFeatureLine(parent, feature)
    f = CreateFrame("FontString ", nil, parent)
    f:Show()
    f:SetText(feature.Name)
    for k, v in pairs(feature.Values) do
        CreateCheckbox(f, v, UseTypeNames[k])
    end
end

function CreateCheckbox(parent, value, ttp)
    b = CreateFrame("CheckButton", nil, parent)
    b:Show()
    b:SetChecked(value)
    b.tooltip = ttp;
end

First of all, CreateFrame("FontString") fails - it writes "Unknown frame type 'FontString'". I am a bit surprised - I expected that every type of xml frame can be created via code.

Second, if I change "FontString" just to "Frame", the code generates no errors but doesn't work - checkboxes do not appear. At the same time, RecommendOptionsFrame is shown correctly (I see it on screen).

And third, I have questions :

1. How to make frame with text using code?
2. Why checkboxes don't appear?
3. Which addon does create its GUI using code? (that I can inspect).