Why yshift doesn't work in this TikZ example?

Question

Any idea why yshift doesn't work in the following TikZ example?

\documentclass{minimal}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}
  \coordinate (A) at (0,0);
  \coordinate (B) at (2.5,0);
  \draw (A) -- (B);
  \draw[yshift=2cm] (A) -- (B);
\end{tikzpicture}

\end{document}

Answer 1

It would work with coordinates or if you place the yshift inside the parentheses next to the name A and B:

\documentclass{minimal}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}
  \coordinate (A) at (0,0);
  \coordinate (B) at (2.5,0);
  \draw (A) -- (B);
  \draw ([yshift=2cm]A) -- ([yshift=2cm]B);
\end{tikzpicture}

\end{document}

Output:

Answer 2

yshift (and similar commands) are applied to all coordinates in the path, not to the path as a whole. They are also not applied to anchors: according to the TikZ manual (section 15.11. in the 2.0 version):

Once the node x has been defined, you can use (x. anchor ) wherever you would normally use a normal coordinate. This will yield the position at which the given anchor is in the picture. Note that transformations do not apply to this coordinate, that is, (x.north) will be the northern anchor of x even if you have said scale=3 or xshift=4cm. This is usually what you would expect.