Package textpos defining textblock in width of \textwidth and relative commands

Question

I have some questions, that won't be solved by the documentation.

1.) [This is solved, solution in 1]I would like to do

\documentclass{scrartcl}
\usepackage{textpos}
\begin{document}
\begin{textblock}{\textwidth}(0,0)
Text of full paperwidth, doesn't matter, if i'd chose a4 to a0
\end{textblock}
\end{document}

but \textwidth doesn't work. My intention is: Defining a fixed block at fixed position of relative width, depending on the chosen paper-size. This leads to my 2nd question.

2.) Is there a way, to declare textblocks orientated on an anchor "top, right" instead of "top, left". Am I able to define anchors for textblock like: top=xx, right=xx. Or bottom=xx, left=xx?

3.) How to set a backgroundcolor to textbox?

4.) How to make the outer-text of textbox don't underlay the textbox? If I declare a Textbox as a heading-element, and inserting something outside of this, i'll achive the following image: The blue bar shows the end of the textbox-environment. So if I do

\begin{textbox}
inner text
\end{textbox}
outer text

I would like to have the "outer text" just below the textbox, so that \clearpage and other commands will still work.

Solution

1 Credits to Jürgen

\documentclass{scrartcl}
\usepackage{textpos}
\begin{document}
\begin{textblock*}{\textwidth}(0cm,0cm)
    Text of full paperwidth, doesn't matter, if i'd chose a4 to a0
\end{textblock*}
\end{document}

[3] Credits to Documentation Using the command below, defines the backgroundcolor of all Textboxes

\textblockcolour{hcolour i}

Credits to Jürgen for giving the hint to:

fcolourbox This will be another solution for just one box.

Answer 1

To question 1)

RTFM: If you like to use absolute values, than you have to use the starred version.

\documentclass{scrartcl}
\usepackage{textpos}
\begin{document}
\begin{textblock*}{\textwidth}(0cm,0cm)
Text of full paperwidth, doesn't matter, if i'd chose a4 to a0
\end{textblock*}
\end{document}

To question 2)

I think with internal means of this package this is not possible. But an idea: One might put the contents of the textblock into a box, measure its height and change the vertical position parameter of the textblock accordingly. Should work, but I am not sure whether this is the most elegant way ...

To question 3)

\textblockcolor is of course the canonical solution. [\fcolorbox is another solution which works independent of this package. It may lead to problems with the correct adjustment inside of textblocks.]