English "qu" and "gu"), but with considered normative. Alveolar consonants t, d, n, l are acceptably either apical (as in English) or laminal (as in French, generally but incorrectly called "dental"). Postalveolars ĉ, ĝ, ŝ, ĵ may be palato-alveolar (semi-palatalized) as in English and French, or retroflex (non-palatalized) as in Polish, Russian, and Mandarin Chinese. H and ĥ may be voiced , especially between vowels. Rhotics The consonant r can be realised in many ways, as it was defined differently in each language version of the Fundamento de Esperanto: In the French Fundamento, it is defined as r. The French rhotic has a wide range of realizations: both the voiced uvular fricative or approximant and the voiceless uvular fricative , the uvular trill , the alveolar trill , and the alveolar tap . These are all recognized as the phoneme , but the trills and the tap are considered dialectal. In the English Fundamento, it is defined as in rare, which is an alveolar approximant . In the German Fundamento, it is defined as r. Most varieties of Standard German are spoken with a uvular rhotic, now usually a fricative or approximant , rather than . The alveolar pronunciation is used in some standard German varieties of Germany, Austria, and Switzerland. In the Russian and Polish Fundamento, it is defined as р (cyrillic), which is most commonly an alveolar trill . The most common realization depends on the region and native language of the Esperanto speaker. For example, a very common realisation in English speaking countries is the alveolar flap . Worldwide, the most common realisation is probably the alveolar trill , which makes some people think it is the most desirable pronunciation. However, it is a common misconception to believe that the alveolar trill is the only correct form. The grammar reference Plena Manlibro de Esperanta Gramatiko considers the velar form to be totally good if it is trilled, and considers the other realisations acceptable. In practice, the different forms are well understood and accepted by experienced Esperanto speakers. Vowel length and quality Vowel length is not phonemic in Esperanto. Vowels tend to be long in open stressed syllables and short otherwise. Adjacent stressed syllables are not allowed in compound words, and when stress disappears in such situations, it may leave behind a residue of vowel length. Vowel length is sometimes presented as an argument for the phonemic status