I have upgrade Expression Engine from 5.3 to 7 after upgrade i am facing Notice like UNDEFINED VARIABLE: HEADER_SORTS ee/ExpressionEngine/View/_shared/table.php, line 320
Above error is faced in Pro Variables. Pro variable is coming from the name Low variables in old version of Expression engine(EE). In new version of Expression Engine the Low variables is the part of Expression engine a core system which remove the dependancy of third party package Low variables as in old version of EE.
If we are going to change in core file by defining constant than it's working fine, but it's not a proper solution as core file will be change any time while we are upgrading the version.