Description:
------------
All around PDO documentation (e.g. [1]) it's suggested that named placeholders use the ":foo" syntax both in SQL code and in parameter binding code.

The former is obviously true, the latter is unclear. Omitting colons has always seemed to work in several drivers but I don't know if it's a behaviour to trust and it doesn't seem to be mentioned in documentation.

Please also check "What are colons in parameter names used for?" [2] at Stack Overflow.

[1] http://php.net/manual/en/pdostatement.bindvalue.php
[2] https://stackoverflow.com/questions/17386469/pdo-prepared-statement-what-are-colons-in-parameter-names-used-for

Test script:
---------------
<?php
$dbh = new PDO('mysql:host=localhost', 'test', 'test', array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,));

$sth = $dbh->prepare('SELECT :text AS greeting FROM DUAL');
$sth->bindValue('text', 'Hello, World!', PDO::PARAM_STR);
$sth->execute();
var_dump($sth->fetch(PDO::FETCH_ASSOC));