fix: exact field-key match in trigger_display_if to prevent false positives

[thisismyurl]

What

trigger_display_if used name.match( displaySrc ) to decide whether a
changed input should trigger visibility changes on display_if siblings.
String.prototype.match() treats its argument as a regex and matches
substrings, so any trigger input whose full HTML name attribute contains
displaySrc as a substring incorrectly fires the display logic.

Reproducer (from #873)

$custom_meta_group = new Fieldmanager_Group([
    'name'           => 'custom_meta_group',  // contains "meta" as a substring
    'serialize_data' => false,
    'children'       => [
        'meta'         => new Fieldmanager_Checkbox(['checked_value' => 'meta']),
        'text_field'   => new Fieldmanager_Textfield(['display_if' => ['src' => 'meta', 'value' => 'meta']]),
        'subject_prefix' => new Fieldmanager_Select([...]),
    ],
]);

When subject_prefix changes, its input name is
custom_meta_group[subject_prefix]. The old code evaluates:

'custom_meta_group[subject_prefix]'.match('meta') != null  // → true!

…because "meta" is a substring of "custom_meta_group". This causes
text_field to be shown or hidden whenever subject_prefix changes,
even though text_field should only react to meta.

Fix

Replace the partial regex match with an exact bracket-key check:

// Before
if ( name && name.match( $( this ).data( 'display-src' ) ) != null ) {

// After
var displaySrc = $( this ).data( 'display-src' );
if ( name && ( name === displaySrc || name.indexOf( '[' + displaySrc + ']' ) !== -1 ) ) {

• name === displaySrc handles top-level Fieldmanager fields whose
  input name is the bare field key (no bracket notation).
• name.indexOf( '[' + displaySrc + ']' ) !== -1 handles nested fields
  where the key is wrapped in brackets (e.g. group[meta]). The
  surrounding brackets ensure [meta] cannot match [meta_info] or
  [custom_meta_group].

Testing

1. Set up the group from the reproducer above.
2. Change subject_prefix — confirm text_field visibility does not change.
3. Check the meta checkbox — confirm text_field shows/hides correctly.
4. Run the existing JS test suite: npm test (or equivalent).

Fixes #873

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates the “display-if” field matching logic in the FieldManager initializer to use explicit string comparisons rather than regex matching.

Changes:

• Replaces name.match(...) regex-based matching with exact-match and bracketed-substring matching.
• Caches display-src in a local variable to avoid repeated jQuery data lookups.

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