Find text between two Markdown headings with regular expression

from Markdown: Regex to find all content following an heading #2 (but stop at another heading #2) - Stack Overflow

/(?:^|\n)##\s[^\n]*\n(.*?)(?=\n##?\s|$)/gs

(?:^|\n)                // make sure we're at the start of a line
##\s                    // match only H2 tags
[^\n]*\n                // skip the heading name
(.*?)                   // match heading content lazily
(?=                     // use a lookahead as to not consume the next heading's start tag
   \n##?\s              // terminate at H1 and H2 headings...
   |$                   // ...or at the end of the file
)