0 a mark put over a vowel in some languages, such as German, to show that the pronunciation of the vowel is changed -- （德语等语言中表示元音发音发生变化的）变音符
In contrast, umlaut is neither a separate segment nor stem final and is thus less salient.
There is also a minor subclass which has a stem alternation other than umlaut.
The same applies to the morphophonological alternations vowel lengthening and umlaut, which are discussed in sections 4.1 and 4.2 below.
There is also a handful of nouns which undergo umlaut on one of their back vowels, but which have other back vowels which are unaffected.
Contrary to what one might expect, it is not the case that both vowels in a diphthong are fronted when umlaut is applied.
All of the former are reconstructed as having had a suffix containing a 'high front unround' segment which 'triggered' the umlaut reflected in these spellings.
Lengthening is a change in the length feature (and\or the tense feature) whilst umlaut fronts back vowels.
An elegant featural statement of umlaut phonology may well be possible, but it is not our concern here.
