The Baybayin script is part of the Unicode standard. In unicode it is called the Tagalog script and is given the 1700-171F range.
The writing system is an abugida system using consonant-vowel combinations. Each character, written in their basic form, is a consonant ending with the vowel "A". To produce consonants ending with the other vowel sounds, a mark is placed either above the consonant (to produce an "E" or "I" sound) or below the consonant (to produce an "O" or "U" sound). The mark is called a kudlit. The kudlit does not apply to stand-alone vowels. Vowels themselved have their own glyphs.
In its original form however, a stand-alone consonant (consonants not ending with any vowel sound) cannot be produced. This was particularly hard for the Spanish priests who were translating books into the native language. Father Francisco Lopez introduced his own kudlit in 1620 that eliminated the vowel sound. The kudlit was in the form of a "+" sign, in reference to Christianity. This cross-shaped kudlit functions exactly the same as the virama in the Devanagari script of India. In fact, Unicode calls this kudlit the TAGALOG SIGN VIRAMA.