ecce | ML Prediction of Bible Topics and Passages | Topic Modeling library

ABC is a music notation; I'm working on patterns to parse it as part of an app.

Sometimes multiple renditions of a tune are in an ABC file, and I need to get just the first rendition -- or in an ideal world any rendition I specify. The beginning of a rendition is signified by the X: string.

It's not possible to know in advance how many renditions are in a file.

In Javascript, how can I return, for example, the first rendition (from the first X: inclusive to the beginning of the second) in the example below, in a way that will return the first if there is no second, and return the first if there are more than two renditions.

My work so far yields ([\s\S]*)(?=X:) which succeeds in the two rendition example, but fails with a single rendition or more than two.

Adding an 'OR'd end of file condition to the lookahead lets the single rendition case work, but fails on the one and three rendition cases, e.g. \([\s\S]*)(?=X:|$)

Any help appreciated ... a good way to parse ABC will be used by many.

A two-rendition example can look like the below -- for a three rendition example just add a line with X: at the end, and for a single chop off everything from the second X:

EDITS: Folks have been kind enough to ask for better examples, and they won't fit in a comment, so here's a few

Broken pledge is interesting because it has more than one ABC and they're not numbered sequentially:

I have n ellipses with foci and eccentricity. The coordinates are in complex format

I am trying to learn C# by making a program that finds two values in which the system becomes equilibrium. I tried the Do-While loop but I can't establish the while statement since the values for the while statement is inside the Do-statement. It just says "The variables does not exist in the current context". I hope I make sense.

Update: The complete code is posted below. I tried the while (true) statement and added a if-break statement. I don't really know if this is how the if-break statement works. The loop goes on and on without end. I tried printing the values but from the very first loop, it already satisfies the conditions.

Below is my code: