How can I put “=” in a TikZ node label specified as an option

Question

When I try to put an = symbol into a TikZ node label specified as an option (using label=), I get an error:

Extra }, or forgotten $.

Is there a way to specify = in such cases that I'm missing?

---

\documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
  \node(x){$X$};
  \path(x)[late options={label=right:=$A$}];     % Works but doesn't display anything
  \path(x)[late options={label=above:$\neq B$}]; % Works 
  \path(x)[late options={label=below:$C$}];      % Works 
  \path(x)[late options={label=left:$=D$}];      % Fails! 
\end{tikzpicture}
\end{document}

Answer 1

Key-value systems look for =, and can't 'tell' that the = here is part of the 'value'. You therefore need braces:

\documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
  \node(x){$X$};
  \path(x)[late options={label={right:=$A$}}];
  \path(x)[late options={label=above:$\neq B$}]; 
  \path(x)[late options={label=below:$C$}]; 
  \path(x)[late options={label={left:$=D$}}]; 
\end{tikzpicture}
\end{document}

(You get an error as the = inside math mode leaves to grouping issues, which don't happen in the first case.)