Default Ignorable

What Are Default Ignorable Code Points?

A Default Ignorable Code Point is a character that should, by default, produce no visible glyph and no advance width when rendered. These characters exist to convey invisible semantic information—joining behavior, direction control, variation selection—without disturbing the visual flow of text when a renderer does not support them.

The rule is: if a process does not recognize or support a default ignorable character, it should silently discard it rather than display a replacement box (□) or a question mark. This allows documents using advanced Unicode features to degrade gracefully on older or simpler systems.

Important Default Ignorable Characters

# ZWJ is used to combine emoji into sequences
family_emoji = "\U0001F468\u200D\U0001F469\u200D\U0001F467"
# MAN + ZWJ + WOMAN + ZWJ + GIRL = 👨‍👩‍👧

print(len(family_emoji))           # 5 code points (including 2 ZWJ)
print(family_emoji)                # Renders as single family emoji on supported systems

# ZWNJ prevents Arabic ligature formation
# ك + ZWNJ + ا → kaf and alef do NOT join
# ك + ا           → normal: join into ـكا

# Soft hyphen: invisible but marks a valid break point
word = "antidis\u00ADestablishment\u00ADarianism"
print(word)     # Visible on most renderers without hyphens
print(len(word))  # 27 code points including 2 SHY

Testing for Default Ignorable

The Unicode property Default_Ignorable_Code_Point (DI) is a derived property. Characters with DI=Yes form a set that includes not just control and format characters but also many reserved code points in the Specials and Tag blocks.

# Using the 'regex' package for property-based matching
import regex
di_pattern = regex.compile(r'\p{Default_Ignorable_Code_Point}')

test = "Hello\u200BWorld"   # contains ZWSP
matches = di_pattern.findall(test)
print(f"Found {len(matches)} default ignorable character(s)")
# Found 1 default ignorable character(s)

Quick Facts