This character should be placed right after the first character in the cluster so a single character spanning across the whole line would be placed and the second inserted character would then be placed in the second line. For example, without inserting the filler, the cluster 𘮦𖿤𘮡𘱆(*siỏ ? iú ui) would appear incorrectly as 𘮦𘮡𘱆.
For fonts which do not combine characters into clusters but just list them one after another, this character has no effect on the placement, but it should act as a normal character and have some appearance to still distinguish between both varieties of clusters.
