A Proposal for Bidi Isolates in Unicode

Section 3.4 (Reordering Resolved Levels): Treat isolate format
codes as whitespace
In Rule L1, items 3 and 4, replace “Any sequence of whitespace characters” with “Any sequence
of whitespace characters and/or isolate format codes (FSI, LRI, RLI, and PDI)”.
In the paragraph introducing the examples, replace “with Bidi Controls and BN characters
removed” with “with BN characters and some Bidi Controls removed”.
Section 4.2 (Explicit Formatting Codes): Add intermediate class
Replace “three classes” with “four classes”. Split the last class (“Full bidirectionality”) with two:
● Non-isolate bidirectionality. The implicit Bidirectional Algorithm, the implicit directional
marks, and the explicit non-isolate directional formatting codes are supported: RLM,
LRM, LRE, RLE, LRO, RLO, PDF.
● Full bidirectionality. The implicit Bidirectional Algorithm, the implicit directional marks, and
all the explicit directional formatting codes are supported: RLM, LRM, LRE, RLE, LRO,
RLO, PDF, FSI, LRI, RLI, PDI.
Section 4.3 (Higher-Level Protocols): Allow isolate emulation
Modify HL3 to include isolates:
● Replace the title (“Emulate directional overrides or embedding codes”) with “Emulate
directional formatting codes”.
● In the body, replace “a directional override or embedding” with “a directional embedding,
isolate, or override”.
Section 5.2 (Retaining Format Codes): Use isolating run sequences
Throughout the section, replace each instance of:
● “sor” with “sos”
● “eor” with “eos”
● “level run” with “isolating run sequence”
Note: I have no idea what “In rule X10, assign L or R to the last of a sequence of adjacent BNs
according to the eor / sor, and set the level to the higher of the two levels” means. It probably
needs editing.
Section 5.5 (Usage): Add isolate usage suggestions
Needs work. We may want to deprecate the embedding formatting codes in favor of isolates.