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 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 any of four grammatically-correct sequences, each with at least four discrete sentences, by adding punctuation: The first two relate a simple philosophical proverb in the style of Parmenides that all that is, is, and that anything that does not exist does not. The phrase