Extended-Tamil script or Tamil-Grantha refers to a script used to write the Tamil language before the 20th century Tamil purist movement. Tamil-Grantha is a mixed-script: a combination of the conservative-Tamil script that independently evolved from pre-Pallava script, combined with consonants imported from a later-stage evolved Grantha script (from Pallava-Grantha) to write non-Tamil consonants. Some scholars posit that the origin of Tamil-Grantha is unclear: the script could also be a direct descendant of the Pallava-Grantha script which extensively developed during the Middle Tamil period to write Middle-Tamil.
The Modern Tamil script is a subset of Tamil-Grantha alphabet, retaining only the 18 consonants taken from Tolkāppiyam-based Old Tamil which generally was written using Vatteluttu script. Tamil-Grantha has 36 consonants, hence covering all Indic consonants like Malayalam script. However, the Modern-Tamil standard allowed a few additional consonants from Grantha into its alphabet: ஜ (ja), ஷ (ṣa), ஸ (sa), ஹ (ha). But their usage is discouraged by Tamil purists and recommend to assimilate the sounds to approximate pure-Tamil phonology, respectively: ச (ca), ச (ca), ச (ca), க (ka). Another letter ஶ was also allowed in 2005 exclusively to write ஶ்ரீ (śrī); however purists enforce the usage of திரு (tiru) over ஶ்ரீ.