Relational Spacing
A group of related glyphs can share a spacing decision. Metrics expressions let one glyph's bearing or width follow another value. Binding holds a bearing to a chosen value while its own outline changes. Use a link for a relationship between metrics, and a binding for a stable clearance around changing content.
Linking Metrics with Expressions
Enter a metrics expression in an LSB, RSB, or Width field in the Metrics Table, property bar, or Glyph panel. The formula defines the relationship; its evaluated number shows the current result. The Contextual widget also displays resolved bearings beside their expressions.
A glyph name links to that glyph's same metric: n follows its LSB when entered in LSB, its RSB in RSB, or its advance in Width. o+10 adds ten units to the corresponding source value. A Unicode character can identify its assigned glyph; a name can identify an unencoded alternate.
Establish the source spacing first, enter the target link, and inspect the result. A small trial source change helps confirm the intended relationship; undo the trial afterward if needed. The receiving field does not edit the source glyph.
An extended expression starts with =. Current-glyph functions l(), r(), b(), and w() give LSB, RSB, metric bounding-box width, and advance width. Named-glyph functions include lsb("n"), rsb("n"), and width("n"). Quote the glyph specifier; arithmetic and parentheses can combine values. For example, =(lsb("n")+lsb("o"))/2 averages two left bearings. F1 over a metrics field provides its syntax help.
| follows the opposite bearing; |n+10 follows the opposite bearing of n plus ten. Keep one side independent to avoid circular links. A colon reference such as :Regular links across layers of the same glyph; see Interpolation and Compatibility. Guide/location expressions use a separate language.
Font > Live Update > Live Metrics controls edit-time updates; Font > Update Glyphs provides an explicit refresh. Check the active master and resulting formulas. Dragging a linked bearing can adjust its offset; entering a plain number replaces the formula. Avoid independent expressions in all three fields: two bearings, drawing width, and advance must agree. Inspect Output messages for unresolved names or cycles.
For a group, choose Font > Metrics > Link Glyph Metrics…, check selection-versus-font scope, and choose the sides and key glyphs. The dialog can compare values or optically compare shapes using a tolerance. Respect script of the left and right key glyphs prevents cross-script links. Apply with OK, then inspect the expressions and text; optical resemblance is a candidate relationship, not proof of correct spacing.
Link Glyph Metrics separates left and right keys and lets you compare shapes or sidebearing values. Review the script, tolerance, and scope choices before applying.
Binding Sidebearings
Without a binding, changing the outline's left or right extent changes its measured clearance. Bind a bearing when you want the clearance to remain fixed while you refine the drawing.
Use Bind left sidebearing or Bind right sidebearing in the Metrics property bar. Each side is independent. For a numeric bearing of 50, binding stores a fixed expression such as =50.
When the outline changes, FontLab can translate the drawing and adjust its advance to restore the bound clearance. Binding does not lock the nodes or promise that the advance width remains fixed. Inspect both bearings and the width after a substantial outline edit.
The = prefix has two related uses: it begins an extended expression, but =50 specifically holds a numeric metric value. It is not a self-reference to whichever bounding-box value happens to exist later. An expression such as =rsb("n")+10 instead depends on another metric.
A field already containing a nonnumeric link is not an ordinary unbound number. Inspect its formula before trying to bind or unbind it; the toggle need not replace an existing expression. To remove an unwanted relationship deliberately, enter the intended numeric result.
Use binding after establishing the clearance you want, and leave it off when you need outline movement to change the bearing freely. The bound value remains subject to the font's metric evaluation and precision behavior. The Nonspacing property and composite metric bounds are taught in Controlling Composite Metrics.