Query: What are, according to the text, murmured for their duration?
Context: Some linguists restrict the double-dot subscript ⟨ ◌̤⟩ to murmured sonorants, such as vowels and nasals, which are murmured throughout their duration, and use the superscript hook-aitch ⟨◌ʱ⟩ for the breathy-voiced release of obstruents.