The component of the syllable which usually contains a vowel. Some languages, English is an example, also allow a small set of syllabic consonants to occur in the syllable nucleus. A further consideration is whether the nucleus can contain more than one segment. Some phonological theories deal with long vowels as two identical vowels dominated by a branching nucleus and diphthongs as non-identical vowels, or a sequence of a vowel + approximant, again dominated by a branching nucleus.