Thinker uses chunky hypertext, where the text is broken up into statements. A statement can include a label, links to other statements by label, and links to external files of various types. Links to flat text files can include an offset and length to look at specific segments of text in the file. A statement that is nothing but a link can be seen through, so you see the text the link references. A statement with subordinate statements can be closed, meaning that the subordinate statements aren't visible. The user can open the statement to see it's subordinate statements.
Thinker supports multiple different threads of control from the user through multiple open windows, using multiple files. Multiple windows can view the same file, but not vice versa. It allows copying, moving and deleting complete subtrees of statements, and sequential groups of subtrees with the same parent.