You can insert a DITA PI marker of type Title in the first paragraph of a split or extract, and supply the text of the title as the marker content. The content of the marker becomes the page title of the split or extract file. You can use macros and macro variables in the marker content.
As an alternative, you can add the Title property to a different marker type: for example, custom marker type Split (see §27.3.1 Designating split points), or custom marker type ExtrStart; and specify the title as the content. See §38. Working with processing instructions for more information.