Example of what happens when a file like www.domain.com/wrong_file.pdf is called using modified class.tslib_fe.php :
NB: there variables listed either side of functions show the vlaues of these variables before & after these functions.
Where the functions are indented further than the preceding function this is due to that function being called inside the previous named function.
in /typo3/sysext/cms/tslib/
$TSFE->checkAlternativeIdMethods() // called from index_ts.php # Since the 'TYPO3_SITE_SCRIPT' is not a valid typo3 SSD page. /*.html
$TSFE->determineId() // called from index_ts.php
$this->id = ''
$this->setIDfromArgV() // class.tslib_fe.php # $this->id must be 'false' in order for any processing to happen in here, BUT sinve there is no alias $this->id is set to 0
$this->id = 0
$this->id = 0
$this->fetch_the_id() // class.tslib_fe.php # Get The Page ID
$this->id = 0
$this->id = 0
$this->checkAndSetAlias() // class.tslib_fe.php # Fetches the integer page id for a page alias.
$this->id = 0
$this->pageNotFound = 0
$this->id = 0
$this->findDomainRecord() // class.tslib_fe.php # Looking up a domain record based on HTTP_HOST
$this->id = 0
$this->id = 0
$this->getPageAndRootlineWithDomain() // class.tslib_fe.php # Gets ->page and ->rootline information based on ->id. ->id may change during this operation.
$this->id = 0
$this->getPageAndRootline() // class.tslib_fe.php # Gets the page and rootline arrays based on the id, $this->id
$this->id = 0
***** // inside this function if $this->id still equals 0 after $this->sys_page->getPage(), and if $this->TYPO3_CONF_VARS['FE']['pageNotFound_handling'] is true then $this->pageNotFoundAndExit() is called
$this->pageNotFound = 1
$this->id = 0
$this->sys_page->getPage() // class.t3lib_page.php # If no page is found an empty array is returned.
$this->id = 0
// inside this function; if $this->id starts with a value of 0, then no page is found and an empty array is returned to function getPageAndRootline()
$TSFE->getConfigArray() // called from index_ts.php