re_config/1 will backtrack through all the possible configuration values if its argument is a variable. If an unknown option is specified, re_config/1 fails.

Non-compatible changes between PCRE1 and PCRE2 because numeric values changed: bsr and newline have been replaced by bsr2 and newline2:

• bsr2 - previously bsr returned 0 or 1; now returns unicode or anycrlf
• newline2 - previously newline returned an integer, now returns cr, lf, crlf, any, anycrlf, nul

Term values are as follows. Some values might not exist, depending on the version of PCRE2 and the options it was built with.

• bsr2 The character sequences that the \R escape sequence matches by default. Replaces bsr option from PCRE1, which is not compatible.
• compiled_widths An integer whose lower bits indicate which code unit widths were selected when PCRE2 was built. The 1-bit indicates 8-bit support, and the 2-bit and 4-bit indicate 16-bit and 32-bit support, respectively. The 1 bit should always be set because the wrapper code requires 8 bit support.
• depthlimit
• heaplimit
• jit true if just-in-time compiling is available.
• jittarget A string containing the name of the architecture for which the JIT compiler is configured. e.g., 'x86 64bit (little endian + unaligned)'.
• linksize
• matchlimit
• never_backslash_c
• newline2 An atom whose value specifies the default character sequence that is recognized as meaning "newline" (cr, lf, crlf, any, anycrlf, nul). Replaces newline option from PCRE1, which is not compatible.
• parenslimit
• stackrecurse
• unicode Always true
• unicode_version The unicode version as an atom, e.g. '12.1.0'.
• utf8 - synonym for unicode
• parens_limit
• version The version information as an atom, containing the PCRE version number and release date, e.g. '10.34 2019-11-21'.

  For backwards compatibility with PCRE1, the following are accepted, but are deprecated:

  • utf8 - synonym for unicode
  • link_size - synonym for linksize
  • match_limit - synonym for matchlimit
  • parens_limit - synonym for parenslimit
  • unicode_properties - always true

  The following have been removed because they don't exist in PCRE2 and don't seem to have any meaningful use in PCRE1:

  • posix_malloc_threshold
  • match_limit_recursion