Subscripts

Huffman (1970:35):

"When two orthographic consonants are pronounced consecutively (without an intervening vowel) within a word, the second (and sometimes, in medial position, a third) consonant symbol is written in a special subscript form below the first symbol. [...] These subscripts are called ជើងអក្សរ /cəəŋ qaqsɑɑ/ 'consonant's feet' in Cambodian [...]."

The Unicode Consortium (2015:614) describes a Khmer subscript as a symbol representing any consonant following the first consonant in an orthographic syllable. The Unicode character used to represent this is called Khmer Sign Coeng ្ [U+17D2]. For instance, to get a Khmer subscript, one should key-in the Khmer Sign Coeng and a consonant right after it (្ + ង /ŋ/ -->  ្ង /ŋ/).
The table below shows a list of consonant and their corresponding subscript underneath each of them. Consonant ឡ does not have a subscript.

Khmer Subscripts