Modification of variables

Hello, everyone. Can anybody help me to understand the meaning of modified[0] and modified[1] and so on. For example, if the position of modif::dataStructure and modified[1] = modif::nothing exchanges what would occur ?

void getTypeOfModification(std::vectormodif::ModifT& modified) const {
modified[0] = modif::dataStructure;
modified[1] = modif::nothing;
}