I think the quickest method is to use guidelines to align accents manually after using Complete Composites with the help of guidelines. It is not precise and takes some care to maintain consistency, but it takes no preliminary work. Editing CompleteComposites.xml is probably best avoided unless you need to add definitions for unsupported composites. Edits that work better for some fonts may not work as well for other fonts or other font styles. If you’re comfortable with editing code it can save time, but if you make a small typo it can break the feature completely.
If you’re adding anchors, then Anchor Based composition does it automatically. It works better across different fonts and type styles, but there are exceptions where the optical centre of a glyph is not at its geometric centre. These exceptions need some work adjusting the anchor points after composition. Use Auto Attach for these composites.
I am still learning how to make the most of Anchor Based composition. There are several preliminary steps needed for it to work as designed.
- Correctly named combining diacritics must be added to the font. The size and vertical position of these glyphs must be correct. The advance width must be zero.
- Tools menu, Glyph Names, Generate should be used. Small Capitals, Petite Capitals, etc., can be renamed quickly using Find and Replace Glyph Names on selected glyphs.
- Code-points in the Private Use Area are no longer needed for alternate glyphs, but Complete Composites now relies on glyph names being correct.
- Auto Attach should be enabled for composites if the anchors of the base glyphs need editing
- Important: Importing scripts from other fonts will remove all anchors unless the OpenType features for Anchor Based Positioning are included. When working on a set of type styles, I export scripts and import them into other styles to avoid duplicating work on adding/editing OpenType features.