@coloncolon

In this website I place the sign "::" between two vowels that are next to each other. These two will be always in different syllables, and nearly always in different words.

Example:

arjuna::uvAca अर्जुन‌उवाच

This is mainly a teaching device intended to make beginners less confused. Usually you don't need to write it yourself.

This a::u अ‌उ means a अ (uh-sound) followed by u उ (short oo-sound).

But an au औ is not an a अ plus an u उ, but a single vowel — khau खौ sounds like "cow".

Therefore writing

arjunauvAca

is a BIG mistake, because there is no "now" (nau नौ) sound in there, it must be na न + u उ.

Similarly ai ऐ is not two vowels, it is a single vowel that sounds like "eye". I use a::i अ‌इ when I mean an a अ ("uh" sound) followed by an i इ (short "ee" sound), but ai ऐ when I mean the "eye" sound —

**sas सस् + **icchati इच्छति → sa::icchati स‌इच्छति

**sA सा + **eva एव → saiva सैव

Can coloncolon appear within a word?

That is extremely uncommon, but it does happen sometimes.

If by "word" you mean /pada —

!**pra::uga- प्र‌उगॱ "triangle" (likely from prayuga- प्रयुगॱ)

If by "word" you mean /samAsa —

**manas- मनस् + icchA- इच्छाॱ → !**mana::-icchA- मन‌ॱइच्छाॱ "mind-desire"

Because it is so uncommon, there is no official harvard-kyoto transcription equivalent of "::". This means that when an online dictionary is using HK internally for its scripting, you may expect mispellings like prauga titau manaicchA EW*pra uga प्र उग to appear in the devanagari देवनगरि.