OpenType Designer - Mark to Base and Mark to Mark
Mark to Base and Mark to Mark are commonly used to add diacritic marks to base 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.
Mark and Base glyphs are connected to each other via so called anchors. Anchors control the behaviour how the mark glyph interacts with the base glyph.
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 where each of the defined mark glyph will be drawn.
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.
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.