Caracteres ZWJ, ZWNJ:

^ = ZWJ (zero width joiner)
^^ = ZWNJ (zero width non joiner)
Usually when a consonant cluster (two or more consecutive consonants) occurs, it will be rendered as a ligature if that is available in the font. The ZWJ and ZWNJ can be used to produce an alternate rendering of the ligatures.
If a consonant is followed by the ZWJ, half-form of the consonant is formed.
Example:
shakti - शक्ति
shak^ti - शक्‍ति
rakShaNa - रक्षण
rak^ShaNa - रक्‍षण

If a dead consonant (consonant with halant symbol) is required, the ZWNJ character should be used after the consonant.
Example:
rAj^^kumAr - राज्‌कुमार
rAjkumAr^^ - राज्कुमार्‌