Are LaTeX's label names case-sensitive? Can label names contain spaces?

Question

According to Guide to LaTeX, 4th edition, when creating a \label{name},

The keyword name may be any combination of letters, numbers, or symbols.

Is the name of a label case-sensitive? Can the name contain spaces?

I'm asking because when using Vim's snipmate TeX snippet, if I type sec and hit tab, I automatically get:

\section{section name}
\label{sec:section name}

Then when I enter the section name in the \section, Vim automatically puts the same text after the sec: portion of the \label. Since my sections are often multiple, capitalized words, the label name ends up containing spaces and are capitalized. For instance, I might get:

\section{Planned Testing}
\label{sec:Planned Testing}

Prior to allowing Snipmate in Vim automatically enter the label name based on the section name, I would have manually typed:

\section{Planned Testing}
\label{sec:planned_testing}

Spaces not allowed

Syntastic in Vim shows an error if a label name contains spaces.

Answer 1

Is the name of a label case-sensitive? Can the name contain spaces?

Yes and yes.

References are stored as a macro using \csname r@<name>\endcsname, so anything allowed within \csname...\endcsname is valid (as reference, see Understanding how references and labels work and What exactly do \csname and \endcsname do?). This includes a distinction between case (since, by nature \macro is different from \Macro, \MaCRo, \MACRO, ...).

As a small example consider:

\documentclass{article}
\expandafter\def\csname some bizarre Name 123\endcsname{Stuff}
\begin{document}
\csname some bizarre Name 123\endcsname

\section{A section}\label{sec:A section}
See~\ref{sec:A section} and~\ref{sec:a section}.
\end{document}