Scope of accidentals in measureless music

1. What is the purpose of accidentals in music?
2. What is the rule for an accidental in music?
3. Do accidentals apply to the whole song?
4. What effect do accidentals have?

What is the purpose of accidentals in music?

But in music, accidentals are notes that add a hint of drama to a measure. Some are sharp, others are flat. Others cancel out a sharp or flat and restore a measure to its earlier key.

What is the rule for an accidental in music?

Accidentals apply to subsequent notes on the same staff position for the remainder of the measure where they occur, unless explicitly changed by another accidental. Once a barline is passed, the effect of the accidental ends, except when a note affected by an accidental is tied to the same note across a barline.

Do accidentals apply to the whole song?

The accidental will apply to following notes in the same measure / bar but not after that. If it is needed to cancel the effect before then another accidental (maybe a natural sign) will be required. Oddly, although a sharp or flat in the key signature affects the same note in other octaves, an accidental does not.

What effect do accidentals have?

Unlike the key signature, an accidental is placed within a measure, just before the altered note. Its effect stops at the end of the measure in which it is placed.