Sometimes I have quite long org-mode documents. I tend to insert new headings and sub-headings throughout the whole document. However sometimes I think that I already used this text and begin searching in the document. The easier way would be to just insert the heading and have org-mode show some warning when this exact text exists somewhere in the document as heading. Currently I think best would be if the color of the heading changes. Is this possible and if yes, how can this be done?