what is Limited durative which is described below?

First, let's consider the most salient function of the Progressive Aspect, which is to refer to TEMPORARY situations, activities, or goings-on:

Where's Joan?' 'She's cooking the dinner.'

'What on earth are you doing?' 'I'm trying to play the violin.'

What's happening?' 'The river's overflowing its banks.'

These examples illustrate the Progressive Present: the temporary situation includes the present moment in its time-span, stretching for a limited period into the past and into the future. To distinguish the Progressive Present as used here from the Simple Present, we need to stress three separate aspects of meaning:

1 The Progressive Form indicates duration (and is thus distinguished from the non-durative 'event present').

2 The Progressive Form indicates limited duration (and is thus distinguished from the 'state present').

3 The Progressive Form indicates that the happening need not to be complete

(and is again thereby distinguished from the 'event present').

• Geoffrey N. Leech (2004). Meaning and the English verb