The text between extended grapheme cluster boundaries as specified by Unicode Standard Annex #29, "Unicode Text Segmentation."

• Extended grapheme clusters are defined in a parallel manner to legacy grapheme clusters, but also include sequences of spacing marks.
• Grapheme clusters and extended grapheme clusters may not have any particular linguistic significance, but are used to break up a string of text into units for processing.
• Grapheme clusters and extended grapheme clusters may be adjusted for particular processing requirements, by tailoring the rules for grapheme cluster segmentation.
• The associated base character is the base character in the combining character sequence that a combining mark is part of.
• A combining mark in a defective combining character sequence has no associated base character and thus cannot be said to depend on any particular base character. This is one of the reasons why fallback processing is required for defective combining character sequences.
• Dependence concerns all combining marks, including spacing marks and combining marks that have no visible display.