in inc/plugins/_plugin.funcs.php

Please consider adding support for the form input placeholder attribute.

before

// Passthrough some attributes to elements:
	foreach( $parmeta as $k => $v )
	{
		if( in_array( $k, array( 'id', 'class', 'onchange', 'onclick', 'onfocus', 'onkeyup', 'onkeydown', 'onreset', 'onselect', 'cols', 'rows', 'maxlength' ) ) )
		{
			$params[$k] = $v;
		}
	}

after

// Passthrough some attributes to elements:
	foreach( $parmeta as $k => $v )
	{
		if( in_array( $k, array( 'id', 'class', 'onchange', 'onclick', 'onfocus', 'onkeyup', 'onkeydown', 'onreset', 'onselect', 'cols', 'rows', 'maxlength', 'placeholder' ) ) )
		{
			$params[$k] = $v;
		}
	}

https://github.com/midnight-studios/b2evolution/pull/2/commits/88f61a9495c2e0460811eff4e85ee7c2cd5175ef