@chsk/annotation is part of a data visualization framework based on @chsk/core. It provides utilities and graphical elements that can be incorporated into any chart type.

• Filters use svg capabilities to fine-tune the appearance of chart components
• Flowchart components such as arrows direct attention toward specific regions
• Labels use decorations such as boxes, brackets, or braces to provide explanations for specific chart elements
• Markers use svg capabilities to display lines with custom symbols such as arrowheads
• Symbols provide a library of shapes for use as standalone elements, points in scatter charts, or in legends
• Export utilities save charts to svg files, optimizing content to achieve small file sizes
• Other miscellaneous components include decorations for grids

See here