Reversing Double Encoded HTML Entities

Broadly speaking, the questions relating to working with HTML usually fall into three categories: generating new HTML, manipulating existing HTML, and analyzing HTML-like documents with other languages embedded in them. The first category is one we are all generally familiar with because the output of most PHP applications is an HTML string, whether produced entirely in PHP or through some other purpose-built templating engine, such as Blade. However, things get particularly interesting and nuanced in the last two categories.