# Escaped characters in typewriter font

I know a number of ways to fix this (e.g. \usepackage[T1]{fontenc}), but I want to understand what's happening in the following example.

\documentclass{article}
\begin{document}
\noindent
\$\% \& \{ \} \_ \# \textbackslash \\ \ttfamily \$ \% \& \{ \} \_ \# \textbackslash \\
\verb+\$ % & { } _ # \ +
\end{document}

• Why does attempting to obtain a \ttfamily brace, underscore or backslash result in the substitution of the ordinary roman symbol? The glyphs are clearly not missing, because verbatim mode can access them.

• How exactly is verbatim mode accessing these glyphs?

• Deleting the braces and the backslash, so that the underscore is the only remaining 'problem' character eliminates the font warnings, despite the fact that a substitution is still taking place. Why is this?

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