You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Estonian_language

Context:
One distinctive feature that has caused a great amount of interest among linguists is what is traditionally seen as three degrees of phonemic length: short, long, and "overlong", such that /sɑdɑ/, /sɑˑdɑ/ and /sɑːdɑ/ are distinct. In actuality, the distinction is not purely in the phonemic length, and the underlying phonological mechanism is still disputed.[citation needed]

Question:
What is a matter of dispute among linguists regarding the distinction?

the underlying phonological mechanism