Inscript keyboard was designed by C-DAC. This keyboard was standardized by the govt. of India for typing Indic text.
Separate keys are used for typing the swara (independent vowel) and the corresponding matra (dependent vowel sign). But, if matra keys are typed alone, swara will be produced instead.
Matra can't be added to an existing consonant. The complete Consonant+Vowel (CV) combination has to be typed at the same time.
The 'a' matra is implicit in the consonants. The key should be used explicitely to add the halant symbol.
The asciicircum key is used for the ZWNJ (Zero Width Non Joiner). The ampersand key is used for the ZWJ (Zero Width Joiner).
These are required in some scripts to produce an alternate rendering of a character in some cases.