Punctuation the marks hierarchically, in terms of weight". Cecil Hartley's poem identifies their relative values: <poem style=margin:4em;> The stop point out, with truth, the time of pause A sentence doth require at ev'ry clause. At ev'ry comma, stop while "one" you count; At semicolon, "two" is the amount; A colon doth require the time of "three"; The period "four", as learned men agree. </poem> The use of punctuation was not standardised until after the invention of printing. According to the 1885 edition of "The American Printer", the importance of punctuation was noted in various sayings by children such as: <poem style=margin:4em;>
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