Each combining character has a combining class property expressed as a numeric value. Combining characters that appear in the same location relative to the base character when displayed will typically share the same combining class. For example acute, grave and circumflex accents all appear above the base character and all share the same combining class.

Multiple combining characters do not have to be in any particular order unless they are in one of the Unicode normalisation forms. The standard requires that sequences of combining characters should be treated as equivalent if they all have different combining classes.

Unicode normalisation, however, applies a canonical ordering to multiple combining characters.

If characters have the same combining class they are likely to interact typographically to produce different possible results, as in the case above. In this case the ‘inside-out’ rule is applied. This rule states that the proximity of the combining character in the text stream must match the visual proximity.