Aristophanes of Byzantium needed to complete each fragment of text when reading aloud (not to comply with rules of grammar, which were not applied to punctuation marks until thousands of years later). For a short passage (a "komma"), a "stigmḕ mésē" dot was placed mid-level (·). This is the origin of the modern comma punctuation mark, and its name. For a longer passage (a "kolon"), a "hypostigmḗ" dot was placed level with the bottom of the text (.), similar to a modern colon or semicolon, and for very long pauses ("periodos"), a "stigmḕ teleía" point near the top of the line of text
That that is is that that is not is not is that it it is was noted in "Brewer's Dictionary of Phrase and Fable". This phrase appeared in the 1968 American movie "Charly", written to demonstrate punctuation to the main character Charly's teacher, in a scene to demonstrate that the surgical operation to make the character smarter had succeeded. That that is is that that is not is not is that it it is That that is is that that is not is not is that it it is is an English word sequence demonstrating syntactic ambiguity. It is used as an example illustrating the importance of proper punctuation. The sequence can be understood as