Secondary alteration, where possible, is shown by a circular "handakuten": "h"→"p"; For example; becomes . Diacritics, though used for over a thousand years, only became mandatory in the Japanese writing system in the second half of the 20th century. Their application is strictly limited in proper writing systems, but may be more extensive in academic transcriptions. Furthermore, some characters may have special semantics when used in smaller size after a normal one (see below), but this does not make the script truly bicameral. The layout of the "gojūon" table promotes a systematic view of kana syllabograms as being always pronounced with the same single consonant followed by a vowel, but this is not exactly the case (and never has been). Existing schemes for the romanization of Japanese either are based on the systematic nature of the script, e.g. nihon-siki チ "ti", or they apply some Western graphotactics, usually the English one, to the common Japanese pronunciation of the kana signs, e.g. Hepburn-shiki チ "chi". Both approaches conceal the fact, though, that many consonant-based katakana signs, especially those canonically ending in "u", can be used in coda position, too, where the vowel is unvoiced and therefore barely perceptible. Of the 48 katakana syllabograms described above, only 46 are used in modern Japanese, and one of these is preserved for only a single use:  A small version of the katakana for "ya", "yu" or "yo" (ャ, ュ or ョ, respectively) may be added to katakana ending in "i". This changes the "i" vowel sound to a glide (palatalization) to "a", "u" or "o", e.g. キャ ("ki + ya") /kja/. Addition of the small "y" kana is called yōon. Small versions of the five vowel kana are sometimes used to represent trailing off sounds (ハァ "haa", ネェ "nee"), but in katakana they are more often used in yōon-like extended digraphs designed to represent phonemes not present in Japanese; examples include チェ ("che") in チェンジ "chenji" ("change"), ファ ("fa") in ファミリー "famirī" ("family") and ウィ ("wi") and ディ ("di") in ウィキペディア "Wikipedia".