IntlChar::isIDStart() function in PHP

The IntlChar::isIDStart() function is used to check whether the entered character is permissible as the first character of an identifier or not.

Syntax

bool IntlChar::isIDStart(mixed $codepoint)

Parameters

• $codepoint − A character or integer value encoded as a UTF-8 string, or an integer representing a Unicode code point.

Return Value

The IntlChar::isIDStart() function returns TRUE if the value is a character that can be used as the first character of an identifier, FALSE otherwise. Returns NULL on failure.

Example

The following example demonstrates checking various characters for identifier start validity −

<?php
    var_dump(IntlChar::isIDStart("Tom"));
    echo "<br>";
    var_dump(IntlChar::isIDStart("9"));
    echo "<br>";
    var_dump(IntlChar::isIDStart("A"));
    echo "<br>";
    var_dump(IntlChar::isIDStart("_"));
    echo "<br>";
    var_dump(IntlChar::isIDStart("$"));
?>

NULL
bool(false)
bool(true)
bool(true)
bool(false)

Key Points

• Letters (A-Z, a-z) and underscores are typically valid identifier start characters

• Numbers (0-9) cannot be the first character of an identifier

• Multi-character strings return NULL as the function expects a single character

• The function follows Unicode identifier rules

Conclusion

The IntlChar::isIDStart() function is useful for validating whether a character can begin an identifier according to Unicode standards. It returns TRUE for valid identifier start characters like letters and underscores, but FALSE for numbers and special symbols.