run-in, run in definition

In CSS, a run-in creates either an inline box or block box, and this is determined by the circumstances.  It is defined by display: run-in.  The outcome is determined by the rules of: 1) If the run-in includes a block-box, the run-in will create a block box. 2) If a sibling block box directly follows a run-in and it is not absolutely positioned or  floated, then the run-in box turns into the sibling block box’s first inline box. 3) The run-in will create a block box if both conditions are not applicable.