It is quite common on the internet (and commonly used on Stack Exchange also) to use a short sentence to resume a longer explanation. There are different ways to express this such as:
Short answer
...
Long answer
... x 100
.
TL;DR: ...
or simply denoting the point without a title.
The question is what would be the best solution to benefit the legibility of the text for the user reading it (I am asking specifically about which part to make bolder/more noticeable):
TL;DR:
The point is this.
vs
TL;DR:
The point is this.
vs
TL;DR:
The point is this.
vs
The point is this.
In my opinion a resumed idea should be kept to a sentence or two, not a paragraph. Also I am referring to resumed ideas, not highlighting of the points through the long answer.