Add feature to the open-source text annotation tool

One of our main tasks at Knowledgator Engineering company is creating datasets for its further usage by Machine Learning programs. 

To create a dataset, we use an open-source annotation tool(http://brat.nlplab.org/examples.html) that helps identify entity types in the text and the fundamental relations between them. After the text is initially annotated by the annotation tool, our employees manually analyze it and add/correct missing entities and relations using the annotation tool features. For example, to highlight an entity in the text, we select a given phase and assign it to the proposed entity type(a country, person, etc.).

We've created plenty of datasets utilizing this open-source annotation tool, and we are planning to keep using it, but we've gathered some improvement suggestions from the employees that we would like to implement.

So our employees often analyze big-size texts, and when using the annotation tool, which visually highlights entities and relations between them, it often becomes very overwhelming to analyze and make corrections to the text when you see a lot of visual elements above the text. 

We want to add an option to enable/disable highlighting relations between entities by default and display it only on-premise when a user selects a particular entity from the text, and then to show only those relations that are assigned to the selected entity. This will allow our employees to analyze texts more efficiently, by reducing that visual overwhelming which is shown by default.

The code of the annotation tool is published here - https://github.com/nlplab/brat. Technically this particular task will require only JavaScript knowledge.

In the picture above is the sample of the text in the annotation tool, which shows the highlighted entities and relations between them.