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XPath Reference
Limitations

Known Limitations

goxpath passes 85% of the W3C QT3 XPath 3.1 conformance tests (~18,900 of ~22,200 applicable tests). The following areas have known gaps.

Regular Expressions

Go’s standard regexp library uses the RE2 engine, which does not support back-references (\1, \2). XPath patterns using back-references will fail with a compile error.

(: NOT SUPPORTED :)
matches("abab", "(ab)\1")     (: back-reference to group 1 :)

Character class subtraction ([a-z-[aeiou]]) is handled by removing the subtracted part, which may produce incorrect results for some patterns.

Integer Precision

xs:integer is stored as Go int (int64), limiting the range to approximately ±9.2 × 10¹⁸. Values beyond this range overflow silently. The XPath specification requires arbitrary-precision integers.

(: May lose precision :)
xs:integer("999999999999999999999")   (: beyond int64 range :)
format-number(1E25, '#')              (: outputs max int64, not 10^25 :)

Decimal Precision

xs:decimal is stored as Go float64, providing ~15-17 significant digits. True arbitrary-precision decimal arithmetic is not implemented.

Timezone Handling

Go’s time.Time does not distinguish between “no timezone specified” and “UTC timezone”. This means:

(: May produce "Z" where no timezone is expected :)
string(xs:time("13:20:00"))     (: may show "13:20:00Z" instead of "13:20:00" :)

Date/time serialization may add or omit timezone indicators in edge cases.

Unicode Collation

The Unicode Collation Algorithm (UCA) is not implemented. Functions that accept a collation argument (compare(), contains(), etc.) accept the argument but use simple codepoint comparison.

Not Implemented

The following XPath 3.1 features are not available:

Feature Notes
fn:transform() Requires XSLT processor integration
fn:xml-to-json() Partial implementation
fn:collation-key() Requires UCA
fn:idref() Requires DTD/Schema ID resolution
try/catch expressions XQuery-only feature (not in XPath 3.1)
Schema-aware types No XML Schema validation
namespace:: axis Not implemented

format-number Gaps

  • Exponent patterns with # as sole integer digit may produce wrong mantissa in edge cases
  • Fraction grouping (#.#,##,#) is not fully implemented
  • Large numbers exceed int64 range
  • Named decimal formats require registration via the Go API (not auto-discovered)

format-date / format-dateTime / format-time Gaps

  • Non-English word formatting ([YWw] in German, French, Italian) is not supported — only English words
  • IANA timezone conversion (5th argument) is not implemented
  • Calendar systems other than ISO are not supported
  • Digit families in timezone output are not translated
Go APILanguage Features