S-groups

Link node

• Structural conditions: The bracket is placed around one atom that has two connecting and crossing bonds
• Value conditions: Range of integers starting from 1 (e.g. 1-4)

Repeating unit

• Structural conditions: The bracket is placed around a fragment with either 1-1 or 2-2 bonds crossing both brackets OR only one of the brackets has crossing bonds
• Value conditions: It must have at least one range of integers and then other ranges and positive integers are accepted (e.g. 0-4; 1-3, 6-8; 3-5, 8; 2, 4-6)

Structural conditions

Description	Example
One attachment point on each bracket
Only one attachment point
Two attachment points on each bracket

Value conditions

Description	Example
Value is multiple ranges
Value is a mix of a range and a number
Value is a mix of ranges and numbers

SRU Polymer

• Structural conditions: The bracket is placed around a fragment with either 1-1 or 2-2 bonds crossing both brackets
• Value conditions: One letter of the english alphabet (e.g. n; m)

Structural conditions

Description	Example
One attachment point on each bracket
Two attachment points on each bracket

Multiple group

• Structural conditions: The bracket is placed around a complete molecule with no attachment points or a fragment with arbitrary number of crossing bonds
• Value conditions: Positive integer (e.g. 4)

Structural conditions

Description	Example
No attachment points
Only one attachment point
Arbitrary number of attachment points

Custom group

• No structural and value conditions. All S-groups that are not fitting in the above listed categories are considered Custom groups.

Description	Example
No attachment points, no value
Arbitrary number of attachment points, special value