In some sans serif typefaces, the uppercase I may be difficult to distinguish from the lowercase letter L, 'l', the vertical bar character '|', or the digit one '1'. In serifed typefaces, the capital form of the letter has both a baseline and a cap height serif, while the lowercase L generally has a hooked ascender and a baseline serif.. The dot over the lowercase 'i' is sometimes called a tittle. More @Wikipedia
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