The Balkan dialects are the most extensive group of dialects of the Bulgarian language, covering almost half of the present-day territory of Bulgaria. Their range includes north-central Bulgaria and most of the Bulgarian part of Thrace, excluding the Rhodopes, the region of Haskovo and Strandzha. As a result of the mass population movements that affected eastern Bulgaria during the 19th and the beginning of the 20th century, the Balkan dialects are now spoken also in vast areas of northeastern Bulgaria, especially the regions of Dobrich and Varna. The most significant feature of the dialects, as in most Eastern Bulgarian dialects, is the pronunciation of Old Church Slavonic ѣ (yat) as ʲa or ɛ, depending on the character of the following syllable. The Balkan dialects, and in particular, the Central Balkan dialect, lie at the foundation of formal Bulgarian. However, they are not identical to the standard language because many of its features derive from the Western Bulgarian dialects, including the Macedonian dialects, or are a compromise between Eastern and Western standard.