Alignment in cases with text outside the cases

Question

How can we align text in nested cases within all cases?

\documentclass[12pt,a4paper]{article}
\usepackage[fleqn]{amsmath}

\begin{document}


\begin{align}
\begin{cases}
Equation 1 = 0 &\text{Align this 1} \\
\begin{cases}
     Equation 2 = 0, &\text{ Align this 2 } \\
     Equation 3 = 0, &\text{ Align this 3 } \\ 
     \end{cases}\\
     Equation 4 = 0, &\text{ Align this 4}
\end{cases}
\end{align}
\end{document}

This produces a "local" alignment within each case, but doesn't align through both cases, which I would like.

Answer 1

Something like this?

\documentclass[12pt,a4paper]{article}
\usepackage[fleqn]{amsmath} % for 'cases' environment

\begin{document}
\begin{equation}
\begin{cases}
  Equation 1 = 0  & \text{Align this 1 } \\
  \left\{ \begin{array}{@{} l @{}} 
          Equation2 = 0 \\
          Equation3 = 0 
  \end{array} \right. &
  \begin{array}{@{}l}
          \text{Align this 2 } \\
          \text{Align this 3 } 
  \end{array} \\
  Equation 4 = 0, & \text{Align this 4 }
\end{cases}
\end{equation}
\end{document}

Answer 2

A slightly different alignment with empheq and blkarray:

\documentclass[12pt,a4paper]{article}
\usepackage[fleqn]{empheq}
\usepackage{blkarray}

\begin{document}

\begin{empheq}[left=\empheqlbrace]{equation}
\raisebox{0pt}[\height][4ex]{ \begin{blockarray}{>{$}l<{$}l}
Equation 1 = 0 & Align this 1 \\
\begin{block}{\{>{$}l<{$}l}
     Equation 2 = 0, & Align this 2 \\
     Equation 3 = 0, & Align this 3 \\
     \end{block}
     Equation 4 = 0, & Align this 4
\end{blockarray}}
\end{empheq}

\end{document}