Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Worksheet/Worksheet.php
public function setCodeName($pValue, $validate = true)
    {
        // Is this a 'rename' or not?
        if ($this->getCodeName() == $pValue) {
            return $this;
        }

        if ($validate) {
            $pValue = str_replace(' ', '_', $pValue); //Excel does this automatically without flinching, we are doing the same

            // Syntax check
            // throw an exception if not valid
            self::checkSheetCodeName($pValue);

            // We use the same code that setTitle to find a valid codeName else not using a space (Excel don't like) but a '_'

            if ($this->getParent()) {
                // Is there already such sheet name?
                if ($this->getParent()->sheetCodeNameExists($pValue)) {
                    // Use name, but append with lowest possible integer

                    if (Shared\StringHelper::countCharacters($pValue) > 29) {
                        $pValue = Shared\StringHelper::substring($pValue, 0, 29);
                    }
                    $i = 1;
                    while ($this->getParent()->sheetCodeNameExists($pValue . '_' . $i)) {
                        ++$i;
                        if ($i == 10) {
                            if (Shared\StringHelper::countCharacters($pValue) > 28) {
                                $pValue = Shared\StringHelper::substring($pValue, 0, 28);
                            }
                        } elseif ($i == 100) {
                            if (Shared\StringHelper::countCharacters($pValue) > 27) {
                                $pValue = Shared\StringHelper::substring($pValue, 0, 27);
                            }
                        }
                    }

                    $pValue = $pValue . '_' . $i; // ok, we have a valid name
                }
            }
        }

        $this->codeName = $pValue;

        return $this;
    }
public function setCodeName($pValue, $validate = true)
    {
        // Is this a 'rename' or not?
        if ($this->getCodeName() == $pValue) {
            return $this;
        }

        if ($validate) {
            $pValue = str_replace(' ', '_', $pValue); //Excel does this automatically without flinching, we are doing the same

            // Syntax check
            // throw an exception if not valid
            self::checkSheetCodeName($pValue);

            // We use the same code that setTitle to find a valid codeName else not using a space (Excel don't like) but a '_'

            if ($this->getParent()) {
                // Is there already such sheet name?
                if ($this->getParent()->sheetCodeNameExists($pValue)) {
                    // Use name, but append with lowest possible integer

                    if (Shared\StringHelper::countCharacters($pValue) > 29) {
                        $pValue = Shared\StringHelper::substring($pValue, 0, 29);
                    }
                    $i = 1;
                    while ($this->getParent()->sheetCodeNameExists($pValue . '_' . $i)) {
                        ++$i;
                        if ($i == 10) {
                            if (Shared\StringHelper::countCharacters($pValue) > 28) {
                                $pValue = Shared\StringHelper::substring($pValue, 0, 28);
                            }
                        } elseif ($i == 100) {
                            if (Shared\StringHelper::countCharacters($pValue) > 27) {
                                $pValue = Shared\StringHelper::substring($pValue, 0, 27);
                            }
                        }
                    }

                    $pValue = $pValue . '_' . $i; // ok, we have a valid name
                }
            }
        }

        $this->codeName = $pValue;

        return $this;
    }
Define the code name of the sheet.

@param string $pValue Same rule as Title minus space not allowed (but, like Excel, change
silently space to underscore)
@param bool $validate False to skip validation of new title. WARNING: This should only be set
at parse time (by Readers), where titles can be assumed to be valid.

@throws Exception

@return Worksheet