refactor: remove three dead file-scoped functions (#330)

A private-scope sweep (a private/fileprivate function with zero in-file
callers is provably dead, with no name-conflation risk) found three:
selectNodes in XSLTTransformer (selectXPathNodes is the live sibling),
processingInstructionMatches in EvaluatorSteps, and parseExternalID in
DoctypeScanner. A doc comment referencing selectNodes was reworded.
Build and 1775 tests confirm no behavior change.

CHANGELOG.md

@@ -13,6 +13,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Two unused private helpers in `XSLTNamespaceFixup` (`fixAttributeName` and `resolvedPrefix`). The result-tree attribute fixup they implemented was inlined into `fix(_ element:)` and evolved past them (the inlined version additionally shadows a carried prefix through `localPrefixes`, which the helpers did not), leaving both with zero callers. Removing them deletes dead, diverged duplicate logic with no behavior change; the live inlined path is unchanged.
 
+- Three more dead file-scoped functions found by a private-scope sweep: `selectNodes` in `XSLTTransformer` (its sibling `selectXPathNodes` is the live one; a doc comment that referenced it was reworded), `processingInstructionMatches` in `EvaluatorSteps`, and `parseExternalID` in `DoctypeScanner`. All three are `private`/`fileprivate` with zero callers, so removing them is provably behavior-neutral (the compiler confirms).
+
 ### Fixed
 
 - A complex type with simple content that restricts a base may no longer relax a base `required` attribute to `optional` (XSD 1.0 `cos-ct-derived-ok` / `derivation-ok-restriction.2`). The attribute-use restriction check ran only over `complexContent` restrictions, so a `simpleContent` restriction that relaxed a required attribute (or added a non-base attribute, or widened the attribute wildcard) was accepted; it now runs over both derivation roots. Closes XSTS `particlesZ030_d`, which libxml2 also rejects, so the fix aligns with the reference rather than exceeding it. XSTS invalid-schemas-accepted 10 -> 9 with valid-schemas-rejected held at 0 (full archive). Guarded by `SimpleContentAttrRestrictionTests`.

Sources/Parsing/DoctypeScanner.swift

@@ -298,22 +298,6 @@ struct DTDScanner {
 }
 
 extension DTDScanner {
-    private func parseExternalID(_ reader: inout Reader) -> ExternalID? {
-        if reader.consume("SYSTEM") {
-            reader.skipSpace()
-            guard let systemID = scanLiteral(&reader) else { return nil }
-            return ExternalID(systemID: systemID)
-        }
-        if reader.consume("PUBLIC") {
-            reader.skipSpace()
-            guard let publicID = scanLiteral(&reader) else { return nil }
-            reader.skipSpace()
-            let systemID = scanLiteral(&reader) ?? ""
-            return ExternalID(publicID: publicID, systemID: systemID)
-        }
-        return nil
-    }
-
     func scanLiteral(_ reader: inout Reader) -> String? {
         guard let quote = reader.peek(), quote == "\"" || quote == "'" else { return nil }
         reader.advance()

Sources/XPath/EvaluatorSteps.swift

@@ -330,12 +330,6 @@ extension PureXML.XPath.Evaluator {
         }
     }
 
-    private static func processingInstructionMatches(_ node: Node, _ target: String?) -> Bool {
-        guard case let .tree(tree) = node, tree.kind == .processingInstruction else { return false }
-        guard let target else { return true }
-        return tree.name?.description == target
-    }
-
     private static func isTreeKind(_ node: Node, in kinds: [PureXML.Model.TreeNodeKind]) -> Bool {
         guard case let .tree(tree) = node else { return false }
         return kinds.contains(tree.kind)

Sources/XSLT/XSLTTransformer.swift

@@ -203,12 +203,8 @@ extension PureXML.XSLT {
             )
         }
 
-        fileprivate func selectNodes(_ expression: String, _ context: XSLTContext) -> [PureXML.Model.TreeNode] {
-            value(expression, context)?.nodes?.compactMap(\.treeNode) ?? []
-        }
-
-        /// Like `selectNodes` but keeping attribute and namespace nodes,
-        /// which templates apply to as well.
+        /// Selects the nodes an expression yields, keeping attribute and namespace
+        /// nodes, which templates apply to as well.
         func selectXPathNodes(_ expression: String, _ context: XSLTContext) -> [PureXML.XPath.Node] {
             value(expression, context)?.nodes ?? []
         }