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International Component for Unicode for Java (ICU4J) is a mature, widely used Java library providing Unicode and Globalization support
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// © 2024 and later: Unicode, Inc. and others.
// License & terms of use: https://www.unicode.org/copyright.html

package com.ibm.icu.message2;

class StringUtils {

    /*
     * abnf: content-char = %x01-08        ; omit NULL (%x00), HTAB (%x09) and LF (%x0A)
     * abnf:              / %x0B-0C        ; omit CR (%x0D)
     * abnf:              / %x0E-1F        ; omit SP (%x20)
     * abnf:              / %x21-2D        ; omit . (%x2E)
     * abnf:              / %x2F-3F        ; omit @ (%x40)
     * abnf:              / %x41-5B        ; omit \ (%x5C)
     * abnf:              / %x5D-7A        ; omit { | } (%x7B-7D)
     * abnf:              / %x7E-D7FF      ; omit surrogates
     * abnf:              / %xE000-10FFFF
     */
    static boolean isContentChar(int cp) {
        return (cp >= 0x0001 && cp <= 0x0008) // omit HTAB (%x09) and LF (%x0A)
                || (cp >= 0x000B && cp <= 0x000C) // omit CR (%x0D)
                || (cp >= 0x000E && cp <= 0x001F) // omit SP (%x20)
                || (cp >= 0x0021 && cp <= 0x002D) // omit . (%x2E)
                || (cp >= 0x002F && cp <= 0x003F) // omit @ (%x40)
                || (cp >= 0x0041 && cp <= 0x005B) // omit \ (%x5C)
                || (cp >= 0x005D && cp <= 0x007A) // omit { | } (%x7B-7D)
                || (cp >= 0x007E && cp <= 0xD7FF) // omit surrogates
                || (cp >= 0xE000 && cp <= 0x10FFFF);
    }

    // abnf: text-char = content-char / s / "." / "@" / "|"
    static boolean isTextChar(int cp) {
        return isContentChar(cp) || isWhitespace(cp) || cp == '.' || cp == '@' || cp == '|';
    }

    // abnf: backslash = %x5C ; U+005C REVERSE SOLIDUS "\"
    static boolean isBackslash(int cp) {
        return cp == '\\';
    }

    /*
     * ; Whitespace
     * abnf: s = 1*( SP / HTAB / CR / LF / %x3000 )
     */
    static boolean isWhitespace(int cp) {
        return cp == ' ' || cp == '\t' || cp == '\r' || cp == '\n' || cp == '\u3000';
    }

    /*
     * abnf: name-start = ALPHA / "_"
     * abnf:            / %xC0-D6 / %xD8-F6 / %xF8-2FF
     * abnf:            / %x370-37D / %x37F-1FFF / %x200C-200D
     * abnf:            / %x2070-218F / %x2C00-2FEF / %x3001-D7FF
     * abnf:            / %xF900-FDCF / %xFDF0-FFFC / %x10000-EFFFF
     */
    static boolean isNameStart(int cp) {
        return isAlpha(cp)
                || cp == '_'
                || (cp >= 0x00C0 && cp <= 0x00D6)
                || (cp >= 0x00D8 && cp <= 0x00F6)
                || (cp >= 0x00F8 && cp <= 0x02FF)
                || (cp >= 0x0370 && cp <= 0x037D)
                || (cp >= 0x037F && cp <= 0x1FFF)
                || (cp >= 0x200C && cp <= 0x200D)
                || (cp >= 0x2070 && cp <= 0x218F)
                || (cp >= 0x2C00 && cp <= 0x2FEF)
                || (cp >= 0x3001 && cp <= 0xD7FF)
                || (cp >= 0xF900 && cp <= 0xFDCF)
                || (cp >= 0xFDF0 && cp <= 0xFFFC)
                || (cp >= 0x10000 && cp <= 0xEFFFF);
    }

    /*
     * abnf: name-char = name-start / DIGIT / "-" / "."
     * abnf:           / %xB7 / %x300-36F / %x203F-2040
     */
    static boolean isNameChar(int cp) {
        return isNameStart(cp)
                || isDigit(cp)
                || cp == '-'
                || cp == '.'
                || cp == 0x00B7
                || (cp >= 0x0300 && cp <= 0x036F)
                || (cp >= 0x203F && cp <= 0x2040);
    }

    // abnf: quoted-char = content-char / s / "." / "@" / "{" / "}"
    static boolean isQuotedChar(int cp) {
        return isContentChar(cp)
                || isWhitespace(cp)
                || cp == '.'
                || cp == '@'
                || cp == '{'
                || cp == '}';
    }

    static boolean isSimpleStartChar(int cp) {
        return StringUtils.isContentChar(cp)
                || StringUtils.isWhitespace(cp)
                || cp == '@'
                || cp == '|';
    }

    // ALPHA is predefined in ABNF as plain ASCII, A-Z and a-z
    // See https://en.wikipedia.org/wiki/Augmented_Backus%E2%80%93Naur_form
    static boolean isAlpha(int cp) {
        return (cp >= 'a' && cp <= 'z') || (cp >= 'A' && cp <= 'Z');
    }

    // DIGIT is predefined in ABNF as plain ASCII, 0-9
    // See https://en.wikipedia.org/wiki/Augmented_Backus%E2%80%93Naur_form
    static boolean isDigit(int cp) {
        return cp >= '0' && cp <= '9';
    }

    // abnf: function = ":" identifier *(s option)
    static boolean isFunctionSigil(int cp) {
        return cp == ':';
    }
}