Mark‑to‑Base, Mark‑to‑Ligature, and Mark‑to‑Mark are commonly used to add diacritic marks to base and ligature glyphs. Mark‑to‑Base and Mark‑to‑Mark are identical in usage, the only difference is that for Mark‑to‑Mark only mark glyphs may be used.
With Mark‑to‑Base, Mark‑to‑Ligature, Mark‑to‑Mark, glyphs are connected to each other via so called anchors. Anchors control the behaviour how the mark glyph interacts with the base glyph.
Note: the number of anchor values used with Mark‑to‑Ligature lookups can be set through the Glyph Properties.
Each base glyph has an anchor point that is defined with the left X and Y value and is indicated by the anchor icon: 
Modifying these values will change the location of the mark glyph.
Each mark glyph also has an anchor point that is defined with the right X and Y value. Modifying these values will change the location of where the mark glyph will be drawn in relation to the base glyph anchor.
In short:
Modify left X,Y: Change position of all marks in relation to the base glyph
Modify right X,Y: Change position of mark in relation to all base glyphs
When used correctly, anchors are a very powerful tool to quickly change the position of several base/mark glyph combinations without having to modify all of your pairs. For example: if you create an anchor for uppercase glyphs and an anchor for lowercase glyphs, you could change the location of the mark of all lowercase glyphs at once, without modifying the uppercase glyphs.
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Moves to the next Base/Mark pair |
Next > |
Moves to the previous Base/Mark pair |
Reset |
Reset the values to their previous values |
Clear |
Set all fields to zero |
All Same |
This will set the same anchor value for all glyphs in the currently selected glyph class |
Combining marks and signs that appear in text not in conjunction with a valid consonant base are considered invalid. In Windows, Uniscribe displays these marks using the fallback rendering mechanism, on a dotted circle. For the fallback mechanism to work properly, a font should contain a glyph for the dotted circle (U+25CC). If this glyph is missing from the font, the invalid signs will be displayed on the missing glyph shape (.notdef).