More explanatory comments

Author: Luke Shaw

src/blosc2/lazyexpr.py

@@ -719,11 +719,13 @@ def visit_Name(self, node):
                         opname,
                         v,
                     ) in localop.operands.items():  # expression operands already in terms of basic operands
-                        newopname = ";" + self.update_func(v)  # add illegal character ;
+                        # add illegal character ; to track changed operands and not overwrite later
+                        newopname = ";" + self.update_func(v)
                         newexpr = re.sub(
                             rf"(?<=\s){opname}|(?<=\(){opname}", newopname, newexpr
                         )  # replace with newopname
-                    node.id = newexpr.replace(";", "")  # remove all illegal characters
+                    # remove all instances of ; as all changes completed
+                    node.id = newexpr.replace(";", "")
                 else:
                     node.id = self.update_func(localop)
             else: