I have a grid container with a fixed width and a single row and column containing a single word. When I use the fr unit to size the column, overflow-wrap: break-word does not wrap the word causing the word in the column to overflow. 
To the best of my understanding and docs,  overflow-wrap: break-word is supposed to break at any point to prevent overflow if there is no acceptable break point. 
Two things seem to fix this. One is to have a px unit for column size. Second is having overflow: hidden on the text container. I observed the same behaviour on Chrome(v73) and Firefox(v66).
Does anybody know the reason behind this behaviour ?
https://jsfiddle.net/vdx90qeg/2/
<div class="container">
  <div class="item1">
    someverylongword
  </div>
</div>
.container {
  display: grid;
  grid-template-columns: 1fr;
  /*using 'px' instead of 'fr' works */
  grid-template-areas: "item1";
  width: 80px;
  border: 1px solid black;
}
.item1 {
  grid-area: "item1";
  overflow-wrap: break-word;
  /* overflow: hidden; */
  /* works when uncommented */
}
 
    