React is a robust, open-source JavaScript library created by Facebook that is used across the globe for building user interfaces, particularly single-page applications. React is an integral part of the web development domain and falls into the 'Tech Skills' category as it is vital for many job roles, particularly for Frontend Developers, Full-Stack Developers, and Software Engineers.

Companies seeking candidates with React skills are looking for professionals capable of building interactive, seamless, and performance-oriented UI components for web and mobile applications. Knowledge of React equips candidates with the capability to handle complex application structures by creating reusable UI components and managing them with states and props. Additionally, understanding of React's component lifecycle, hooks, and context API is often desired.

Skills in React also imply proficiency in JavaScript, as it is the foundation of this library. Therefore, a solid understanding of JavaScript concepts such as closures, prototypes, and ES6 features like classes, destructuring, and arrow functions is essential. As React utilizes a virtual DOM to boost application performance, knowledge about how the DOM works can be an added advantage.

Another pivotal trait expected from applicants with React skills is the ability to work with APIs to fetch and post data, often using the 'fetch' or 'axios' libraries. An understanding of states and props routing, often through libraries like React Router or Reach Router, is also essential in managing application views.

A strong acumen in JSX syntax, which is a blend of JavaScript and XML, is also an inherent aspect of React knowledge; JSX simplifies the construction of UI components. Familiarity with CSS and other styling techniques necessary for frontend development is also expected from candidates skilled in React.

Learning or mastering React often demands some complementary skills or tools, including Redux or MobX for state management, libraries like Formik for form handling, an understanding of server-side rendering (SSR), experience with front-end testing libraries like Jest or testing-library, and knowledge of GraphQL.

In conclusion, proficiency in React involves several competencies, and acquiring this skill can significantly improve one's employability in an increasingly competitive technological world. As React continues to be a front-runner in the UI library market, demand for these skills is expected to remain high in the foreseeable future.