[Fizzlemizz]

Rusmikey: Think of each .lua file as a function in its own right and each file is passed several (currently two paramters). The first is the name of the addon the file is in and, the second is a table that is exclusive to and available to all .lua files under the addon. The table can be used for sharing data/functions etc. between .lua files in the addon.

When you see something like local _,Core = ... (usually) near the beginning of a .lua file, that is the "file" retrieving these "parameters" (as mentioned, the _ is usualy used as a throwaway parameter)

function Code.lua(...)
     local _, Core = ...
--or 
    local addonName, Core = ...
--or
   local Addon, NS = ...
end

The UIRadioButtonTemplate doesn't do anything on it own other than just display a checkbutton that looks like a radio button. You have to add the OnClick code to de-select the other buttons when each one is clicked.

<CheckButton name="UIRadioButtonTemplate" virtual="true">
        <Size>
            <AbsDimension x="16" y="16"/>
        </Size>
        <Layers>
            <Layer level="BACKGROUND">
                <FontString name="$parentText" inherits="GameFontNormalSmall" parentKey="text">
                    <Anchors>
                        <Anchor point="LEFT" relativePoint="RIGHT">
                            <Offset>
                                <AbsDimension x="5" y="0"/>
                            </Offset>
                        </Anchor>
                    </Anchors>
                </FontString>
            </Layer>
        </Layers>
        <NormalTexture file="Interface\Buttons\UI-RadioButton">
            <TexCoords left="0" right="0.25" top="0" bottom="1"/>
        </NormalTexture>
        <HighlightTexture file="Interface\Buttons\UI-RadioButton" alphaMode="ADD">
            <TexCoords left="0.5" right="0.75" top="0" bottom="1"/>
        </HighlightTexture>
        <CheckedTexture file="Interface\Buttons\UI-RadioButton">
            <TexCoords left="0.25" right="0.5" top="0" bottom="1"/>
        </CheckedTexture>
</CheckButton>