Question

What are the unicode groups and block ranges that can be specified in character class \p{name}?

e.g.

\p{IsGreek}

Where Is the list of names & description available?

Answer 1

Regular-Expressions.info has lists.

You can also ask the man pages of PCRE itself:

Sets of Unicode characters are defined as belonging to certain
scripts. A character from one of these sets can be matched using a
script name. For example:

\p{Greek}
\P{Han}

Those that are not part of an identified script are lumped together
as “Common”. The current list of scripts is:

Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo,
Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Cham,
Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret,
Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian,
Glagolitic, Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul,
Hanunoo, Hebrew, Hiragana, Imperial_Aramaic, Inherited,
Inscriptional_Pahlavi, Inscriptional_Parthian, Javanese, Kaithi,
Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao, Latin, Lepcha,
Limbu, Linear_B, Lisu, Lycian, Lydian, Malayalam, Meetei_Mayek,
Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic, Old_Persian,
Old_South_Arabian, Old_Turkic, Ol_Chiki, Oriya, Osmanya, Phags_Pa,
Phoenician, Rejang, Runic, Samaritan, Saurashtra, Shavian, Sinhala,
Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le,
Tai_Tham, Tai_Viet, Tamil, Telugu, Thaana, Thai, Tibetan,
Tifinagh, Ugaritic, Vai, Yi.