4.5.4.1 Overview of object-specific horizontal spacing tweaks
Layout objects that have a horizontally fixed position are called items, as opposed to spanners, and for the purpose of horizontal spacing, are grouped into columns. Note heads and rests, forming the main musical material, together with those objects that are logically linked to them – accidentals, articulations, stems, dots, etc. – are all part of ‘musical column’. Prefatory items, such as clefs, time signatures and bar lines, are grouped into ‘non-musical columns’. In the following example, musical items are colored red, while non-musical items are blue.
![[image of music]](../02/lily-f6bb0337.png)
This example shows that there is an alternation between musical and non-musical columns. The first non-musical column contains a clef and a time signature. The first musical column has a note head with its stem and articulation. The second non-musical column is empty and thus is removed during the layout process. The second musical column has a note again. The third non-musical column contains a clef, a bar line and a rehearsal mark, etc.
Within one column, spacing is fixed. On the other hand, the amount of space between consecutive columns is flexible. As we shall see, the methods to adjust spacing within a column and between columns are different.