. In the case of , puts it in the "palatalized" column. This can mean that it is either palatalized alveolar or alveolo-palatal . may actually also be alveolo-palatal , rather than just palatal. The rhotic can be either alveolar or uvular, either a trill or, more commonly, a flap/tap . The glottal stop appears only as an intervocalic separator. As in the Slavic languages with which Yiddish was long in contact (Russian, Belarusian, Polish, and Ukrainian), but unlike German, voiceless stops have little to no aspiration; unlike many such languages, voiced stops are not devoiced in final position. Moreover, Yiddish has regressive voicing assimilation, so that, for example, ('says') is pronounced and ('foreword') is pronounced . Vowels The vowel phonemes of Standard Yiddish are: are typically near-close respectively, but the height of may vary freely between a higher and lower allophone. appears only in unstressed syllables. The last two diphthongs may be realized as and , respectively. In addition, the sonorants and can function as syllable nuclei: אײזל 'donkey' אָװנט 'evening' and appear as syllable nuclei as well, but only as allophones of , after bilabial consonants and dorsal consonants, respectively. The syllabic sonorants are always unstressed. Dialectal variation Stressed vowels in the Yiddish dialects may be understood by considering their common origins in the Proto-Yiddish sound system. Yiddish linguistic scholarship uses a system developed by Max Weinreich in 1960 to indicate the descendent diaphonemes of the Proto-Yiddish stressed vowels. Each Proto-Yiddish vowel is given a unique two-digit identifier, and its reflexes use it as a subscript, for example Southeastern o11 is the vowel /o/, descended from Proto-Yiddish */a/. The first digit indicates Proto-Yiddish quality (1-=*[a], 2-=*[e], 3-=*[i], 4-=*[o], 5-=*[u]), and the second refers to quantity or diphthongization (−1=short, −2=long, −3=short but lengthened early in the history of Yiddish, −4=diphthong, −5=special length occurring only in Proto-Yiddish vowel 25). Vowels 23, 33, 43 and 53 have the same reflexes as 22, 32, 42 and 52 in all Yiddish dialects, but they developed distinct values in Middle High German; Katz (1987) argues that they should be collapsed with the −2 series, leaving only 13 in the −3 series. Comparison with German In vocabulary of Germanic origin, the differences between Standard German and Yiddish pronunciation are mainly in the vowels and diphthongs. All varieties of Yiddish lack the German front rounded vowels and , having merged them with and , respectively. Diphthongs