xSY/HEEVR: clarify use of multiple algorithms

[christoph-conrads]

Checklist

• [x] The documentation has been updated.
• [x] If the PR solves a specific issue, it is set to be closed on merge.

[christoph-conrads]

Changes to the draft in #997:

• replaced double-hyphens ("em dashes") with colons because double-hyphens look ugly in monospace fonts
• avoid a word repetition ("influences")