a numeric context, you get a normal increment. If, however, the
variable has been used in only string contexts since it was set, and
has a value that is not the empty string and matches the pattern
-C</^[a-zA-Z]*[0-9]*$/>, the increment is done as a string, preserving each
+C</^[a-zA-Z]*[0-9]*\z/>, the increment is done as a string, preserving each
character within its range, with carry:
print ++($foo = '99'); # prints '100'