There are many practices and elements of one or another practice under the name of khecarī–mudrā, for the reason that in India every spiritual path introduced something of its own. For example, in Gorakh-bānī, khecarī-mudrā is one of eight mudrās:
मुष मध्ये षेचरी मुद्रा, स्वाद विस्वाद ले उतपनी |
स्वाद विस्वाद समो कृत्वा, मुद्रा तौ भई ||
muṣ madhye ṣecarī mudrā, svād visvād le utapanī |
svād visvād samo kṛtvā, mudrā tau bhaī ||
«Khecarī-mudrā is inside the mouth, where a feeling of pleasant and unpleasant taste appears. Khecarī-mudrā is realised when a practitioner is in even attitude to pleasant and unpleasant tastes.»
Some of these eight mudrās are described in a similar way, as a form of regulation of sensory states.
In Jogpradīpikā by Jayatarāma, which is also written in dialect, khecarī-mudrā is included in the category of several mudrās, which resemble hand mudrās of Śrīvidyā by their names. There are such mudrās as: सर्वसंक्षोभिणी मुद्रा (sarvasaṃkṣobhiṇī mudrā), सर्वविद्राविणी मुद्रा (sarvavidrāviṇī mudrā) etc. They are presented in the same sequence as in Śrīvidyā Tantra, with the difference that in Jogpradīpikā those are not hand gestures, but internal yogic processes. In Śrīvidyā, these mudrās are also associated with various Goddesses (Yoginis), who are worshiped with mantras and also those gestures. Obviously, these elements of Śrīvidyā Ttantra, as well as the elements of other Tantric systems, have influenced yogic methods. Another text that I found in the Nath Chaungera Mandir in Nepal, is Gorakh-yog-mañjarī, which also describes those mudrās. The text is a combination of elements of Hatha-yoga-pradīpikā and possibly Jogpradīpikā. In the yogic khecarī-mudrā description, in the same manner as in Jogpradīpikā, can be found such approaches as चलन calana (a movement of the tongue for stretching of its base), दोहन dohana (stretching), छेदन chedana (cutting the base of the tongue). In the same text, the practices of khecarī-mantra are given with viniyoga, aṅga– and kara-nyāsas.
ॐ अस्य श्री खेचरीमन्त्रस्य कपिल ऋषिः सिद्धिनाथो देवता खेचरीमुद्राप्रसादे सिद्धयर्थे जापे विनियोगः
oṃ asya śrī khecarīmantrasya kapila ṛṣiḥ siddhinātho devatā khecarīmudrāprasāde siddhayarthe jāpe viniyogaḥ
With the declaration of content and the purpose of a sādhana, in the form of success in chanting the mantra, ṛishi, Devatā.
गं हृदयाय नमः| सं शिरसे स्वाहा | नं शिखायै वषट् | मं कवचाय हुं | फं नेत्रत्रयाय वौषट् | लं सः अस्त्राय फट्|
gaṃ hṛdayāya namaḥ| saṃ śirase svāhā | naṃ śikhāyai vaṣaṭ | maṃ kavacāya huṃ | phaṃ netratrayāya vauṣaṭ | laṃ saḥ astrāya phaṭ|
Then recommendations are given to perform kara-nyāsa by adding the following bijas: ह्रं ह्रीं ह्रूं ह्रैं ह्रौं ह्रः hraṃ hrīṃ hrūṃ hraiṃ hrauṃ hraḥ to each element of the kara-nyāsa.
Similar recommendations are given in Yogakuṇḍalyupaniṣaḍ:
पूर्वं बीजयुता विद्या ह्याख्याता याति दुर्लभाम् ॥ ३७ ॥
तस्याः षडङ्गं कुर्वीत तया षट्स्वरभिन्नया ।
कुर्यादेवं करन्यासं सर्वसिद्ध्यादिहेतवे ॥ ३८ ॥
pūrvaṃ bījayutā vidyā hyākhyātā yāti durlabhām ॥
tasyāḥ ṣaḍaṅgaṃ kurvīta tayā ṣaṭsvarabhinnayā ।
kuryādevaṃ karanyāsaṃ sarvasiddhyādihetave ॥ 38 ॥
«This is a special knowledge, described earlier, with the bija which is difficult to implement. It is necessary to perform ṣadaṅga (nyāsa) with an addition of six “svāras” of vowels (previously mentioned as ह्रं ह्रीं ह्रूं ह्रैं ह्रौं ह्रः hraṃ hrīṃ hrūṃ hraiṃ hrauṃ hraḥ. To achieve perfection, one must perform kara-nyāsa.»
Khecarī-mantra is described in Haṭha-tattva-kaumudī (Ch.18) in same way as in Yogakuṇḍalyupaniṣaḍ, and viniyoga, nyāsa with the dhyāna are also given. Five lakhs (500 thousand times) of mantra is recommended to recite for its realisation. The bija-mantra ह्रीं hrīṃ is described as the main khecarī-bija in the following way:
व्याख्यातं खेचरीबीजं तेन योगः प्रसिध्यति ।
vyākhyātaṃ khecarībījaṃ tena yogaḥ prasidhyati ।
«Khecarī means ह ha (i.e. the element of space), र ra or ‘repha’ is the state of fire, so ई–कार ī-kāra is adorned with the space of the moon (i.e. bindu or anusvāra). This way khecharī-bija ह्रीं hrīṃ, which grants perfection in yoga, is formed».
In addition, several more mantras are given. For example, to remove obstacles and please Deities, the following mantra is mentioned:
ह्रीं खेचर्यै नमः hrīṃ khecaryai namaḥ
The melana-mantra in Yogakuṇḍalyupaniṣaḍ is the same as in Khecharī Vidyā of Ādinātha:
ह्रीं भं सं पं फं सं क्षं hrīṃ bhaṃ saṃ paṃ phaṃ saṃ kṣaṃ
However, there are many sources where mantras or bijas, khecharī kūṭākṣaras are very different.
In Gorakh-yog-mañjarī there is a mantra:
ॐ ह्रीं गं सः नमः oṁ hrīṁ gaṁ saḥ namaḥ
In Yogacūḍāmaṇyupaniṣaḍ, khecharī is mentioned in connection with the “So-Ham” mantra:
जाग्रन्नेत्रद्वयोर्मध्ये हंस एव प्रकाशते ।
सकारः खेचरी प्रोक्तस्त्वंपदं चेति निश्चितम् ॥ ८२॥
हकारः परमेशः स्यात्तत्पदं चेति निश्चितम् ।
सकारो ध्यायते जन्तुर्हकारो हि भवेद्धृवम् ॥ ८३॥
jāgrannetradvayormadhye haṃsa eva prakāśate ।
sakāraḥ khecarī proktastvaṃpadaṃ ceti niścitam ॥ 82॥
hakāraḥ parameśaḥ syāttatpadaṃ ceti niścitam ।
sakāro dhyāyate janturhakāro hi bhaveddhṛvam ॥ 83॥
«In the awakened state the so-ham shines in the centre of the eyebrow. The produced sound “Sa” is known as khecharī, it symbolises the state of tvam (the individual Self). The pronounced sound “Ha” means the Supreme Lord, it symbolises tat (That). Who contemplates himself as “Sa” becomes definitely identified with “Ha”(That, i.e. Absolute).»
In Kubjikā Tantra khecharī-bija is called ख्फ्रें khphreṃ, in Tantrāloka Abhinavagupta associated this bija with dissolution in the macrocosm, the practices of Bhairava-mudrā (the unity of outer and inner spaces), etc. There is an instruction given for each element of that bija in Tantrāloka. The Yogi in a state of total renunciation must immerse himself into the space of ‘Kha’, reaching full bloom पुल्ल pulla (‘Pha’ symbol). Individuality will be dissolved in the fire of ‘Ra’ of the triangle (yoni), symbolised by the “E”-phoneme (ए), letting a yogi reside in the great reality of bindu “M”.
In Mahākāla-saṃhitā there are many khecharī-mantras, such as ख्रौं khrauṃ and others. We can consider khecharī as the Goddess, where ‘mudrā‘ is the term of the feminine gender and means ‘a Goddess’, in this sense it can be Kuṇḍalinī itself, ascending into the space above the head, identical to Śiva. In that case she is also a Goddess Śambhavi (Śambhavi-mudrā), i.e. directed to Śambhu – Śiva’s name meaning someone who is manifested as the pacification ‘Śam’. In that context, khecharī-mudrā is the internal process of Śiva-Śakti merging. The mudrā can also mean ‘joy’ (ānanda) of the Goddess and Śiva union. In Kashmir Śaivism, khecharī is a union (mudrā) of the space of our consciousness ‘Kha’ with carana (something that moves within this consciousness or changes, i.e. Śakti). In the texts of KŚ खेचरी khecarī is described among four special mudrās, such as करङ्किणी (karaṅkiṇī), क्रोधिनी (krodhinī), भैरवी (bhairavī), लेलिहाना (lelihānā). Their meditative practices are described in Vijñāna Bhairava Tantra and other texts. The experiences of those mudrās are related to the five centres of the body: kanda (a place where Kuṇḍalinī is in a contracted state), nābhi (abdominal area), hṛdaya (heart), kaṇṭha (throat) and khecharī is comprehended in the bhrumadhya (a point between the eyebrows). It corresponds to the Haṭha-yoga texts, because khecharī is mainly associated with the space of the head or above it. Those mudrās, as well as others are described in detail in āhnika 34 of Tantrāloka, devoted to mudrās. But all the mudrās are considered as manifestations of khecharī, and this also fits with how khecharī is presented in the Yogic texts. In truth, many of Yogic texts, especially some particular parts of them, I personally associate with Tantric processes, which are expounded in Tantras. Here is an example, the part of Yogakuṇḍalyupaniṣad:
तस्मात्सर्वप्रयत्नेन गोपनीयं विजानता । यत्रास्ते च गुरुर्ब्रह्मन्दिव्ययोगप्रदायकः ॥ १४॥
तत्र गत्वा च तेनोक्तविद्यां संगृह्य खेचरीम् । तेनोक्तः सम्यगभ्यासं कुर्यादादावतन्द्रितः ॥ १५॥
अनया विद्यया योगी खेचरीसिद्धिभाग्भवेत् । खेचर्या खेचरीं युञ्जन्खेचरीबीजपूरया ॥ १६॥
खेचराधिपतिर्भूत्वा खेचरेषु सदा वसेत् |
tasmātsarvaprayatnena gopanīyaṃ vijānatā ।
yatrāste ca gururbrahmandivyayogapradāyakaḥ ॥ 14॥
tatra gatvā ca tenoktavidyāṃ saṃgṛhya khecarīm ।
tenoktaḥ samyagabhyāsaṃ kuryādādāvatandritaḥ ॥ 15॥
anayā vidyayā yogī khecarīsiddhibhāgbhavet ।
khecaryā khecarīṃ yuñjankhecarībījapūrayā ॥ 16॥
khecarādhipatirbhūtvā khecareṣu sadā vaset |
«The practitioner must consider a transmission of that practice from a Guru as a connection with Acyuta (Viṣṇu), it is necessary to perceive the Guru, transmitting that secret knowledge, as Śiva himself. Having received that knowledge, it cannot be shared with anyone. Oh Brahman, it’s required to come to the place where that Guru teaches divine yoga and receive khecharī-vidyā from him. After that one can practice very keenly, and khecharī will give him siddhi. “Connecting” युञ्जान yuñjāna with khecharī, through khecharī and khecharī-bija, a yogi becomes a lord of the khecarās and resides in the space all the time (unconditioned).»
This part reminds me of gaining of śaktipāta and transmission of a sādhana, described in Tantrāloka, where śaktipāta is firstly transmitted from a Guru and the knowledge of how to practice. Then a sādhaka receives śaktipāta from a Goddess “Duti”, connecting with her, and that second śaktipāta is considered stronger (तीव्र शक्तिपात tīvra śaktipāta) then the first (मन्द शक्तिपात manda śaktipāta), it gives the highest realisation. Although of course, one cannot be realised without the other, but there is nothing higher then śaktipāta from the Goddess itself.