Build, test, and debug regular expressions
Matches LaTeX display math blocks enclosed in double dollar signs ($$...$$). The body may contain any characters except unescaped dollar signs, parentheses, and backslashes, though escaped sequences (backslash followed by any character) are permitted. Commonly used in Markdown renderers with KaTeX/MathJax to detect math expressions, with the global flag finding all occurrences in a document.