Simple nested environment problem

Question

I thought this would be simple, and it may be but I'm missing something. The following (non-functional code) gives this error:

./mwe-environments.tex:28: LaTeX Error: \begin{innerii} on input line 28 ended by \end{inneri}.

What am I missing? I'd like outer to begin inneri, have innerii conclude inner1 and, finally have \end{outer} finish innerii. (This is a bare-bones MWE -- there is a lot going in in the environments.)

\documentclass{article}

\usepackage{xparse}
\usepackage{calc}

\NewDocumentEnvironment{myouter}{}{%
    \begin{inneri}
}{%
    \end{innerii}
}

\NewDocumentEnvironment{inneri}{}{%
    \bfseries
}{%
}

\NewDocumentEnvironment{innerii}{}{%
    \end{inneri}
    \itshape
}{%
%
}

\begin{document}

\begin{myouter}
Bla bla bla
\begin{innerii}
BLA bLA bLA
\end{myouter}

\end{document}

Answer 1

As David says, doing this is not recommended as it breaks the LaTeX \begin{env}...\end{env} paradigm that everyone expects. This said, here is another way to fix the issue: rather than using \begin{inneri} and \end{inneri} inside the environments just use \inneri and \endinneri. This stops LaTeX from looking ahead and searching for an \end{inneri}. The full code:

\documentclass{article}

\usepackage{xparse}
\usepackage{calc}

\NewDocumentEnvironment{myouter}{}{%
    \inneri
}{%
    \end{innerii}
}

\NewDocumentEnvironment{inneri}{}{%
    \bfseries
}{%
}

\NewDocumentEnvironment{innerii}{}{%
    \endinneri
    \itshape
}{%
%
}

\begin{document}

\begin{myouter}
Bla bla bla
\begin{innerii}
BLA bLA bLA
\end{myouter}

\end{document}

Answer 2

LaTeX is very flexible but if you bend it this much, it might snap, but this runs without error.

\documentclass{article}

\usepackage{xparse}
\usepackage{calc}

\makeatletter
\NewDocumentEnvironment{myouter}{}{%
    \begin{inneri}%
}{%
% please don't do this in any public package
% it completely breaks latex syntax and any editors, syntax
% highlighters or humans trying to read the document.
   \def\@currenvir{innerii}%
    \end{innerii}%
}

\NewDocumentEnvironment{inneri}{}{%
    \bfseries
}{%
}

\NewDocumentEnvironment{innerii}{}{%
% please don't do this in any public package
% it completely breaks latex syntax and any editors, syntax
% highlighters or humans trying to read the document.
    \def\@currenvir{inneri}%
    \end{inneri}%
    \itshape
}{%
%
}
\makeatother
\begin{document}

\begin{myouter}
Bla bla bla
\begin{innerii}
BLA bLA bLA
\end{myouter}

\end{document}