This guide explains regex execution failures and error reporting for schema patterns in Draft 7 and Draft 2020-12.
Regex execution failures
Schema regexes used by pattern, propertyNames, and patternProperties are
subject to the Erlang regex engine's execution limits. If a match exhausts a
limit, JSONSchex stops validation and returns {:error, [error]} with
error.rule == :indeterminate_pattern, rather than treating it as a non-match.
This failure cannot be inverted by not or suppressed by other combinators.
The same protection applies when additionalProperties classifies keys against
patternProperties, including cached matches.
JSONSchex uses the engine's default execution limits. It does not retry matches with input-dependent or automatically increased limits.
Error details
The error's path identifies the affected instance, value and context.input
contain the string being matched (the property name for object-key matches), and
context.error_detail contains the engine reason, such as :match_limit or
:match_limit_recursion.
Avoiding excessive backtracking
Even valid data is rejected if the engine cannot complete the match. Rewrite
patterns with excessive backtracking; for example, ^(?:(a+)+b|a+!)$ can be
replaced with ^a+[b!]$.