No extensions.
As defined in the specifications: https://www.khronos.org/registry/gles/specs/2.0/GLSL_ES_Specification_1.0.17.pdf Swizzles are highlighted if more than one component is used.
The followind highlights groups are used:
- Number
- Comment
- Operator
- Type
- Keyword
- PreProc
- Special
- Constant
- Function