Fix comment to accurately describe non-atomic alternation support

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs

@@ -1992,9 +1992,11 @@ void EmitSwitchedBranches()
                                     break;
                             }
 
-                            // This is only ever used for atomic alternations, so we can simply reset the doneLabel
-                            // after emitting the child, as nothing will backtrack here (and we need to reset it
-                            // so that all branches see the original).
+                            // This is only ever used for alternations where no branch may backtrack
+                            // (whether due to being atomic or simply because nothing in the branch
+                            // can backtrack), so we can simply reset the doneLabel after emitting the
+                            // child, as nothing will backtrack here (and we need to reset it so that
+                            // all branches see the original).
                             doneLabel = originalDoneLabel;
 
                             // If we get here in the generated code, the branch completed successfully.

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexCompiler.cs

@@ -2096,9 +2096,11 @@ void EmitSwitchedBranches(RegexNode node, int childCount, int minValue, int rang
                             break;
                     }
 
-                    // This is only ever used for atomic alternations, so we can simply reset the doneLabel
-                    // after emitting the child, as nothing will backtrack here (and we need to reset it
-                    // so that all branches see the original).
+                    // This is only ever used for alternations where no branch may backtrack
+                    // (whether due to being atomic or simply because nothing in the branch
+                    // can backtrack), so we can simply reset the doneLabel after emitting the
+                    // child, as nothing will backtrack here (and we need to reset it so that
+                    // all branches see the original).
                     doneLabel = originalDoneLabel;
 
                     // If we get here in the generated code, the branch completed successfully.