The augment t is added optionally to a long vowel final in a full word (pada) when followed by cha,
This allows option where by the last it would have been compulsory to add it. The augment is of the long vowel and not of the word ending in long vowel. Thus कूटीच्छाया or कुटीछाया, कूवलीच्छाया or कुवलीछाया ॥ The तुक् augment here is added to the end of a pada, and this is therefore a padanta rule and not a pada-vidhi. Therefore the two words need not be in construction for the application of this rule; (समर्थ पदविधि) not applying. Thus तिष्ठतु कुमारीच्छत्रं हर देवदत्तस्य, \let the girl stay. Take the umbrella of Devadatta\. Here कुमारी and छत्रं are not in construction, but तुक् is still added optionally.
Vart:- The augment त is optional in the Chhandas, after the words विश्वजन &c. As, विश्वजनच्छत्रम् or विश्वजनछत्रम्, नच्छायां कुरवोपराम् or नछायां कुरवोपराम् ॥,