Where is defined ob_start() in Laravel project?

Occurrences of 'ob_start' in Directory /Users/jimm/GitHub/laravel5 with mask '*.*'
Found Occurrences
Unclassified occurrence
laravel5
vendor/aws/aws-sdk-php/src
functions.php
            ob_start();
TraceMiddleware.php
        ob_start();
vendor/cboden/ratchet/tests/unit/Server
EchoServerTest.php
        ob_start();
vendor/doctrine/common/lib/Doctrine/Common/Util
Debug.php
        ob_start();
vendor/doctrine/common/tests/Doctrine/Tests/Common/Util
DebugTest.php
        ob_start();
        ob_start();
vendor/doctrine/dbal/lib/Doctrine/DBAL/Tools/Console/Command
RunSqlCommand.php
        ob_start();
vendor/guzzle/guzzle/phing/tasks
GuzzlePearPharPackageTask.php
        ob_start();
        ob_start();
vendor/guzzle/guzzle/tests/Guzzle/Tests/Plugin/Log
LogPluginTest.php
        ob_start();
vendor/guzzlehttp/guzzle/src
functions.php
            ob_start();
vendor/intervention/image/src/Intervention/Image/Gd
Encoder.php
        ob_start();
        ob_start();
        ob_start();
vendor/laravel/framework/src/Illuminate/View
Factory.php
            if (ob_start()) {
vendor/laravel/framework/src/Illuminate/View/Engines
PhpEngine.php
        ob_start();
vendor/phpdocumentor/reflection-docblock/tests/phpDocumentor/Reflection/DocBlock/Tag
MethodTagTest.php
        ob_start();
vendor/phpoffice/phpexcel/Classes/PHPExcel/Writer
Excel2007.php
                    ob_start();
Excel5.php
                        ob_start();
                        ob_start();
                    ob_start();
vendor/phpoffice/phpexcel/Documentation/markdown/Overview
08-Recipes.md
        ob_start();
vendor/phpseclib/phpseclib/phpseclib/Crypt
RSA.php
                    ob_start();
vendor/phpseclib/phpseclib/phpseclib/Math
BigInteger.php
            ob_start();
vendor/phpunit/phpunit/src/Framework
TestCase.php
        ob_start();
vendor/phpunit/phpunit/src/Util/PHP/Template
TestCaseMethod.tpl.dist
ob_start();
vendor/phpunit/phpunit/tests/Regression/GitHub/1437
Issue1437Test.php
        ob_start();
vendor/psy/psysh/src/Psy/ExecutionLoop
Loop.php
                    ob_start(
vendor/ramsey/uuid/src
Uuid.php
        ob_start();
vendor/sameer-shelavale/multi-captcha/src/types/gif
gif.php
            ob_start();
        ob_start();
vendor/sameer-shelavale/multi-captcha/src/types/image
image.php
        ob_start();
vendor/swiftmailer/swiftmailer/tests/unit/Swift/Plugins/Loggers
EchoLoggerTest.php
        ob_start();
        ob_start();
vendor/swiftmailer/swiftmailer/tests/unit/Swift/Plugins/Reporters
HtmlReporterTest.php
        ob_start();
        ob_start();
        ob_start();
vendor/symfony/console/Tests
ApplicationTest.php
        ob_start();
vendor/symfony/console/Tests/Output
NullOutputTest.php
        ob_start();
vendor/symfony/debug
ExceptionHandler.php
        ob_start(array($this, 'catchOutput'));
            ob_start(array($this, 'cleanOutput'));
vendor/symfony/debug/Tests
DebugClassLoaderTest.php
        ob_start();
ExceptionHandlerTest.php
        ob_start();
        ob_start();
        ob_start();
        ob_start();
        ob_start();
vendor/symfony/http-foundation/File/MimeType
FileBinaryMimeTypeGuesser.php
        ob_start();
vendor/symfony/http-foundation/Tests
ResponseTest.php
        ob_start();
vendor/symfony/http-kernel
Client.php
        ob_start();
vendor/symfony/http-kernel/HttpCache
HttpCache.php
            ob_start();
vendor/symfony/http-kernel/Tests/DataCollector
DumpDataCollectorTest.php
        ob_start();
        ob_start();
        ob_start();
vendor/symfony/http-kernel/Tests/EventListener
DumpListenerTest.php
        ob_start();
vendor/symfony/http-kernel/Tests/Fragment
InlineFragmentRendererTest.php
                ob_start();
        ob_start();
vendor/symfony/process
Process.php
        ob_start();
vendor/symfony/process/Tests
SimpleProcessTest.php
        ob_start();
vendor/symfony/var-dumper/Cloner
VarCloner.php
                ob_start();
vendor/symfony/var-dumper/Tests
CliDumperTest.php
        ob_start();
        ob_start();
HtmlDumperTest.php
        ob_start();
Usage in comments
laravel5
vendor/symfony/var-dumper/Cloner
VarCloner.php
            // check if we are nested in an output buffering handler to prevent a fatal error with ob_start() below

Tank you @jimmck , can we use ob_start() everywhere in our php projects? for example laravel use it in:

vendor/laravel/framework/src/Illuminate/View/Engines PhpEngine.php ob_start();

Is it correct?