इतः अग्रे आपञ्चमाध्यायपरिसमाप्तेः ५।४।१६० इति यावत् {प्रत्ययः} इति संज्ञात्वेन अधिक्रियते।
The above lists the scope of what is called. All those after this sUtra, up to
५।४।१६० प्रत्यय-s are prescribed. The terminology is used as in the sUtra-s
"प्रत्ययलोपे प्रत्ययलक्षणम् १।१।६१ "" etc.
त्रम्॥ धातोः॥
३।१।९१॥ आ तृतीयाध्यायपरिसमाप्तेः (३।४।११७) धातोः इति अयम् अधिकारः वेदितव्यः। {तव्यत्तव्यानीयरः ३।१।९६} इत्यादिकं वक्ष्यति, ते धातोः एव उत्पत्स्यन्ते॥
The prefixes than conjugation forming personal suffixes तिङ् and its substitution, added to the धातु are called in general कृत् suffixes:
कृदतिङ्॥ ३।१।९३|| अस्मिन् धात्वधिकारे तिङ् भिन्नाः प्रत्ययाः कृत्संज्ञकाः भवन्ति
which are used in active voice and other meaning denoting different कारक-s. "कर्तरि कृत्"
http://sanskritdocuments.org/learning_tools/sarvanisutrani/3.4.67.htm Those suffixes from the above सूत्र onward up to
इति ण्वुल्तृचौ ३।१।१३३ इति are called कृत्य प्रत्यय-s. These technical terms are most useful in assessing the meaning of the words so derived. Now to coming to the सूत्र prescribing अनीयर्
तव्यत्तव्यानीयरः occurs as the 96th sUtra in this section 3.1. And hence it is affixed to the verbal root along with two other suffixes tavyat, tavya (both differ in accentuation of the word in Vedic usage) to form future/present passive participle in the meaning of लोट् and some more modification of meaning. The modification of the verbal participle is as follows:
And this suffix is the second one, in the list of कृत्य suffixes, the first being तव्य. कृ+तव्य - कर्तव्यम्, कृ+अनीय - करणीयम् - etc.
Here these are explained briefly तयोरेव कृत्यक्तखलर्थाः ३।४।७०. तयोरेव भावकर्मणोः कृत्यसंज्ञाकाः all the suffixes called कृत्य, क्त and खल् are prescribed in the sense of passive form भाव - for intransitive verbs and कर्म for transitive verb.
Thus, कर्तव्यम्, and करणीयम् - means the thing to be done (as the verb कृ is transitive).
भवता खलु कन्या वोढव्या, वाह्या, वहनीया। भवान् खलु कन्याया वोढा। भवान् खलु कन्यां वहेत्। भवानेतदर्हतीति।
The above illustrates the different shades of कृत्य suffixes. including अनीय in the sense the object (of the verb) deserves to do (the action denoted by the verb) along with other finite conjugated forms. The girl deserves to be married by you. In this case you deserve to marry this girl is the direct translation, than the passive voice.
Hope this is clear. Any doubt will be